[fish heads]

Yes, but you meant it as a joke, like the classic dictionary jape, but in this case it's just a rather dull fact

[Boboff]

But he might have been being Ironic, and meaning that he meant to play on the old joke, or perhaps

He didn't check, he cracked a joke, then you sad acts went and checked, because you don't understand that whether it was true or not, implied or otherwise as to be factual, it was a JOKE. [which don't have to be based in fact]

[Console]

it was a JOKE. [which don't have to be based in fact]

It may have been a joke, but the fact that 'gullible' isn't in wikipedia is actually funnier that the joke he cracked; it's not particularly funny of course, but neither was the 'joke'.