I think it's an excellent precedent to set, actually.  The guy even admitted he did it.  I don't know how many false positives you're going to get anyway.  It would have to be an extremely improbable coincidence for two posts to be written independently like what OP got busted for.  Changing a few words in a post in order to not get caught for plagiarism is still plagiarism.  As hilarious pointed out, it's also very sneaky too.

No loss to the community that this guy got banned, and any false-positives that are for posts that crappy aren't a loss either.  It's very sad that someone would have to use such a shitpost as the basis for plagiarism.  

Good, it serves you right.  All your base.  Are belong to us.