Celsus didn't know the Acta Pilati

[Giuseppe]

But, he continues, no calamity happened even to him who condemned him, as there did to Pentheus, viz., madness or discerption. And yet he does not know that it was not so much Pilate that condemned Him (who knew that for envy the Jews had delivered Him), as the Jewish nation, which has been condemned by God, and rent in pieces, and dispersed over the whole earth, in a degree far beyond what happened to Pentheus.

https://www.newadvent.org/fathers/04162.htm

Hence, for Celsus, Pilate condemned Jesus, but without exonerating himself from a such action.

[Secret Alias]

Not necessarily. Might have known the story but known also it was junk.

[Giuseppe]

Celsus respected Dionysus precisely because he punished Pentheus.

Accordingly, if Celsus had known about the punition/conversion of Pilate (as reported by Acta Pilati), then he would have not despised Christ for the missed punition/conversion of Pilate.