Not to mention simply searching for common file names would do the trick, too. It is not too hard to come up with an algorithm that can return a boolean (or float) indicating if a file collection looks like TV series. "Game of Thrones - S??E??" is a good start.
Then you should explicitly use a product that encrypts before upload. Again, it's not clear that a human at MS looked at anything. They could simply have run a query "does any customer have files looking like TV series".
Run a report that selects the top 0.01% of users by total storage used, return % of space per file extension.