You can’t just jokingly say “this is a robbery” in a bank though.

If you have any familiarity with the kind of people seriously spreading these kinds of conspiracy theories, you'll know that framing "truth bombs" as jokes is par for the course because it creates plausible deniability.

If it really is a joke, what is the punchline? How does it work? What's being made fun of? That it would be outrageous for someone to say that seriously? As "red pillers" like to say: keep making jokes until the joke really lands (i.e. accustom people to hearing it by framing it as a crass joke so they'll no longer flinch when it is said in earnest).

Ah yes, the "humor" of repeating an obscure antisemitic conspiracy theory. It's "funny" because it's obscure enough that the majority of the audience will assume it to be innocent, and liable to jump to the the speaker's defense against the apparent "crazies" who take offense. Like a silent fart, the "joke" is on the audience, and a smile merely indicates that the author is amused.