IIUC, Eusebius is the source for both Aristion/Ariston/Aristo/'Aριστίων, in
Eccl hist. 3.39.4-7, and Aristion/Ariston/Aristo/'Aριστίων of Pella, in
Eccl hist. 4.6.3.
Eccl hist.
3.39:
1. There are extant five books of Papias, which bear the title 'Expositions of Oracles of the Lord' ...
2. But Papias himself in the preface to his discourses by no means declares that he was himself a hearer and eye-witness of the holy apostles, but he shows by the words which he uses that he received the doctrines of the faith from those who were their friends.
3. He says: "
But I shall not hesitate also to put down for you along with my interpretations whatsoever things I have at any time learned carefully from the elders and carefully remembered, guaranteeing their truth. For I did not, like the multitude, take pleasure in those that speak much, but in those that teach the truth; not in those that relate strange commandments, but in those that deliver the commandments given by the Lord to faith, and springing from the truth itself.
4. "
If, then, any one came, who had been a follower of the elders, I questioned him in regard to the words of the elders — what Andrew or what Peter said; or what was said by Philip, or by Thomas, or by James, or by John, or by Matthew, or by any other of the disciples of the Lord; and what things Aristion and the presbyter John, the disciples of the Lord, say. For I did not think that what was to be gotten from the books would profit me as much as what came from the living and abiding voice."
5. It is worth while observing here that the name John is twice enumerated by him. The first one he mentions in connection with Peter and James and Matthew and the rest of the apostles, clearly meaning the evangelist; but the other John he mentions after an interval, and places him among others outside of the number of the apostles, putting
Aristion before him, and he distinctly calls him a presbyter.
6. This shows that the statement of those is true, who say that there were two persons in Asia that bore the same name, and that there were two tombs in Ephesus, each of which, even to the present day, is called John's. It is important to notice this. For it is probable that it was the second, if one is not willing to admit that it was the first that saw the Revelation, which is ascribed by name to John.
7. And Papias, of whom we are now speaking, confesses that he received the words of the apostles from those that followed them, but says that he was himself
a hearer of Aristion and the presbyter John. At least he mentions them frequently by name, and gives their traditions in his writings. These things, we hope, have not been uselessly adduced by us.
https://www.newadvent.org/fathers/250103.htm
and
https://www.biblegateway.com/resources/ ... ion-Aristo
.
That raises the question: what was it that Papias heard from Aristion (and 'the presbyter John')?
- Some unspecified "doctrines of the faith" as per Eccl hist. 3.39.1 ??
Eccl hist.
4.6 says Aristo of Pella said that "the emperor gave orders that [the whole Jewish nation] was prohibited from and should not even see from a distance the land of their fathers"
1. As the rebellion of the Jews at this time grew much more serious, Rufus, governor of Judea, after an auxiliary force had been sent him by the emperor, using their madness as a pretext, proceeded against them without mercy, and destroyed indiscriminately thousands of men and women and children, and in accordance with the laws of war reduced their country to a state of complete subjection.
2. The leader of the Jews at this time was a man by the name of Bar
.cocheba (which signifies a star), who possessed the character of a robber and a murderer, but nevertheless, relying upon his name, boasted to them, as if they were slaves, that he possessed wonderful powers; and he pretended that he was a star that had come down to them out of heaven to bring them light in the midst of their misfortunes.
3. The war raged most fiercely in the eighteenth year of Adrian, at the city of Bithara, which was a very secure fortress, situated not far from Jerusalem. When the siege had lasted a long time, and the rebels had been driven to the last extremity by hunger and thirst, and the instigator of the rebellion had suffered his just punishment, the whole nation was prohibited from this time on by a decree, and by the commands of Adrian, from ever going up to the country about Jerusalem. For the emperor gave orders that they should not even see from a distance the land of their fathers. Such is
the account of Aristo of Pella.
4. And thus, when the city had been emptied of the Jewish nation and had suffered the total destruction of its ancient inhabitants, it was colonized by a different race, and the Roman city which subsequently arose changed its name and was called Ælia, in honor of the emperor Ælius Adrian. And as the church there was now composed of Gentiles, the first one to assume the government of it after the bishops of the circumcision was Marcus.
https://www.newadvent.org/fathers/250104.htm
.
Both accounts raise the prospect the two Aristos were at least contemporaneous (and may have been the same person)
Pella is said to have been within the eastern foothills of the Jordan Valley, close to the modern village of Ṭabaqat Faḥl, only 27 km (17 miles) south of the Sea of Galilee (Lake Tiberias).
IIUC, the first mention of a 'flight to Pella' is by Eusebius in
Eccl hist.
3.5.3, followed by a somewhat-related, fairly rhetorical & even polemic narrative (with reference to "the history written by Josephus"):
But the people of the church in Jerusalem had been commanded by a revelation, vouchsafed to approved men there before the war, to leave the city and to dwell in a certain town of Perea called Pella. And when those that believed in Christ had come there from Jerusalem, then, as if the royal city of the Jews and the whole land of Judea were entirely destitute of holy men, the judgment of God at length overtook those who had committed such outrages against Christ and his apostles, and totally destroyed that generation of impious men.
4. But the number of calamities which everywhere fell upon the nation at that time, the extreme misfortunes to which the inhabitants of Judea were especially subjected, the thousands of men, as well as women and children, that perished by the sword, by famine, and by other forms of death innumerable — all these things, as well as the many great sieges which were carried on against the cities of Judea, and the excessive sufferings endured by those that fled to Jerusalem itself, as to a city of perfect safety, and finally the general course of the whole war, as well as its particular occurrences in detail, and how at last the abomination of desolation, proclaimed by the prophets
[Matthew 24:15-6; Daniel 9:27], stood in the very temple of God, so celebrated of old, the temple which was now awaiting its total and final destruction by fire — all these things any one that wishes may find accurately described in the history written by Josephus.
https://www.newadvent.org/fathers/250103.htm
. 
.