They are taking a sample and matching it up against THEIR OWN DATABASE.
I don't know if they have a db of all these random followers, I'm just saying the query limit is not limiting the application because if you had to send a new query for each follower you still couldn't analyze 500 of them
There's a database of accounts they already have but surely they do something for new accounts and so forth
So just cause Akademics made a twitter app once and bumped up against that limitation doesn't mean there aren't various ways to get around it using different API calls, different data providers, caching and all that