If it's because I mentioned that Altman is gay - and I can't find another reason - I think that's relevant in context of Musk's recent hard shift rightward and his consistently aggressive, unprovoked behavior toward LGBTQ people. For some reason the topic looms large in his mind.
(I don't exactly keep up with Musk's doings, though.)
https://nymag.com/intelligencer/2022/12/elon-musk-smears-for...
One of several similar specifically anti-gay run-ins if you poke around a bit
This kind of stuff matters when it's amplified to 100M+ people, and he knows it.
I put some of the blame for the Club Q nightclub shooting that happened a few weeks later (https://www.nbcnews.com/nbc-out/out-politics-and-policy/club...) on this kind of behavior. There's no evidence the shooter saw that tweet in particular, but his homophobia was clearly stoked by this sort of edgelord-ism on social media.
I think a more likely interpretation is that a lot of people here are Musk fans, and don't like it when he gets criticized, thus downvoting your comment
I'm neither an ultra fanboy nor someone who despises him