Given the further claim of Irenaeus that Jesus lived to well over 40 years old this would appear to be what Irenaeus genuinely believed and not a copyist's error.For Herod the king of the Jews and Pontius Pilate, the governor of Claudius Caesar, came together and condemned Him [Jesus] to be crucified.
I'm suggesting a possible explanation for the idea that Jesus died in the reign of Claudius. There is an early tradition that the apostles only went out from Jerusalem to preach the Gospel 12 years after the death of Jesus. (Apollonius according to Eusebius Preaching of Peter according to Clement of Alexandria etc). This implies that they went out from Jerusalem early in the reign of Claudius. However Irenaeus uses Acts to argue that the apostles were sent out on the Day of Pentecost following the crucifixion. https://www.newadvent.org/fathers/0103301.htm
Irenaeus may be trying to combine the idea of the apostles being sent out at the beginning of the reign of Claudius with the idea of the apostles being sent out on the Day of Pentecost.For, after our Lord rose from the dead, [the apostles] were invested with power from on high when the Holy Spirit came down [upon them], were filled from all [His gifts], and had perfect knowledge: they departed to the ends of the earth, preaching the glad tidings of the good things [sent] from God to us, and proclaiming the peace of heaven to men, who indeed do all equally and individually possess the Gospel of God.