Because they would have obviously known it was their friend making a joke.

I don't think they could have known for sure it was a joke.

The judge’s point is that if they want to sue anyone for misleading them, it should be whoever sent them the message. He’s not saying they would necessarily win that hypothetical case.

So why shouldn't Snapchat (who presumably reported it to the government) be charged for the same offense of reporting a non-threat?

I'm not suggesting they should be, but just following the same logic as your comment.

I thought they might have been talking about reporting a false threat, or something of that nature?

If you are a comedian working on a joke and write one about a political assassination in your private journal, certainly you can't be charged with communicating a threat, because you did not communicate it. But if a friend/enemy finds your notebook, knows you have no intent to harm, but reports the journal to authorities out of spite anyways, then the friend could be culpable for communicating a false threat, even though the joke is in your handwriting. Maybe they were getting at something like that?

In any case, it was very awkward wording at best for a report from Reuters, it should have been either explained or left out.