Exactly. Shadow banning, when done right and very carefully, can be extremely effective against spammers. The trick is that you have to go out of your way to identify false positives correctly so that you don't accidentally do it to a legitimate user. You have to be very careful with it.
Manual review can't be that hard. They don't strike me as a huge scale, the author indicated the system wasn't tripped yet. Seems just about perfect for that scale.
