Basically Kimmel implied that it was a MAGA person. He did not say it was confirmed, so he could just as well have been implying his opinion rather than that it was a fact he knew for certain- the opinion that he thought it was a MAGA person, which was not a good thing to be saying, but is different than confirming it as if it were a known fact that the he had adequate reason to be sure of. That kind of irresponsibility happens all of the place in the news these days, much less commentary situations like this; we would have to censor a lot of people to stop that sort of spin. Most anyone would have thought he was opining that it was MAGA person rather than confirming it. It would have otherwise been explicit rather than just an implication, with some more details.
In other words, it was a dick thing to say given the circumstances and timing, but the idea of censoring it for misinformation is ridiculous. There have been a lot of people (including people in the news on both sides) falsely calling it the other side in many previous incidents well beforehand.