This is a 3rd party developer forum, general help regarding things like this should go to https://help.twitch.tv
To answer your question though, the help site has details on username changes and how inactive usernames get recycled https://help.twitch.tv/customer/portal/articles/1015624-username-rename-and-recycling-policies
Just because a user has few followers, or isn’t following many people, or doesn’t have a bio, is not a sign that the user is inactive, there are many Twitch users who use Twitch like that and it’s a perfectly valid way to use the platform. The fact that the account is still around and hasn’t been removed already for inactivity could be a sign that the account is still in use.