It seems like GH admins are capable of looking at a user and making a judgement call (no repos, no activity, no SSH keys, and a few forks) to determine that the

It seems like GH admins are capable of looking at a user and making a judgement call (no repos, no activity, no SSH keys, and a few forks) to determine that the username is being squatted. And based on the article, the author was just name squatting. I don't think there's a distinction between "legitimate" or not - use it or lose it.