The issue with AI-produced text is rarely bad grammar these days (if anything, that's a marker of human-written text now!), but rather stiff-sounding constructions that humans don't actually use. In this case — semicolons are grammatically correct, but very few people actually use them them (same for em-dashes like what I just used, but you can pry them from my cold, dead fingers).

I absolutely use semicolons when writing professionally. They're just basic parts of grammar, and if you want to be taken seriously by some parts of the world (academia, I'm glaring angrily at you), you would use them.

I guess it comes down to expectations? You don't expect formal conventions from a website writer, while I absolutely do.

I find it interesting that it was a flag for AI writing for you. That's going to make me consider my voice in certain situations now.

I’d expect people writing for a living to understand and use semicolons.