Of course “fake” GitHub accounts are a thing. Just like people pump up their resumes in general. What you’re describing may simply be people who heard that having a GitHub profile with some stuff on it was a good idea. So they uploaded a bunch of projects and got their friends to “like” them. At least I’d personally like to think that people who are actively out to “cheat” on their GitHub repos genuinely put a little more effort into it than that.

I’m not sure if it constitutes as a red flag, but you can always take a look to see if the repo “starring” goes both ways, or/and ask about it.