It would have to go before a court. I think it wouldn't be too hard to convince a jury (or judge) that a head-in-a-basket AI art + description is expression (first amendment) and not a threat

Edit: your first link is a genuine threat. the second one is a picture of someone holding a photo-realistic, mangled head. The head-in-a-basket is neither

You should stay away from this, in case you haven't figured it out. You're not even in the ballpark of a correct understanding of this situation. Better to just think you could argue your way out of this with a deficient understanding of the law than to put it to the test and find out how wrong you are in a courtroom.