UD documents existing connotations of words and expressions. That you don't think it's an actual dictionary doesn't change the fact that those connotations exist.
"sky tweet" is also a stupid name since a tweet is already the name for a post on a very specific platform.
I'm not sure I get why "sky tweet" is a stupid name. "Tweet" was a pretty arbitrarily chosen name for a post on Twitter, but now that "tweet" is a pretty established word, it seems reasonable to use a portmanteau based on that word for a platform based on that platform.
Though in practice I think "skeet" was a bit of a fad to be provocative, and most people just call them tweets, even on bluesky.
"sky tweet" is also a stupid name since a tweet is already the name for a post on a very specific platform.