Guy, it's by an anon and follows the patterns of other jokes in the Talmud. It's a pagan, a Roman, and a Jew walking into a seance. It's already advertised as incongruous because the questionable Jew conducting the seance shouldn't have been doing so in the first place. The punchline is that even though all are speaking of torment the first two say to fight the Jews and the third says to convert to Judaism because he still likes the Jews. It has nothing to do with any theology and is more closely related to any American joke about any conspicuous person going to hell when people don't know theologically if s/he did or not.

You just commented on genetic fallacy. References to names can be determined based on context. I looked at all the Yeshu passages, there are three men named Yeshu from three different centuries (including Jesus) who each have their own passages, then there are a couple passages like this one that just mention Yeshu generically. The pagan is Balaam, who could've meant other people who had been compared to Balaam, and the Roman is Titus, who could've been father Titus Vespasian or son Titus Caesar. So it's a generic reference, not a specified person; it probably reflects on all three Yeshu figures.

There are also quite a few ladies named Mary in the Bible and I have never gotten them all straight. Every time the Bible says Mary it refers to one of them actually doing the thing it says she did. But there are debates about how many and whether some were the same person, and there are questions about some passages which person identified from elsewhere was intended. And Gittin 57a is a passage from which the particular Yeshu can not be specifically identified; in fact there are at least four readings for the name of the Jew (blank, Yeshu, Yeshu of Nazareth, and a sinner of Israel), so we can't insist on which is the original, though I think "Yeshu" is the likeliest. We can infer that some Jews regarded the passage (nonbindingly) as referring to Jesus of Nazareth, but we cannot infer that that is the original Talmudic text given that the Talmudists poke equal fun at three Yeshu figures.

I appreciate your challenges, but they might be better formed as questions rather than as an appeal to ignorance and a false equivalence. You might take the hint that, since I literally found 53 misquotes of this passage and listed them in the link, I might have a bit of evidence of the joke claim therein.