He did it weird then. He should have edited the quote, and put a bolded "s" after the "fail".
But even so, hes attempting to point out something that isn't there, and on top of that, hes using that term in an incorrect context.
B-17's, thats spelling-fail, which is completely different from linguistics-fail. Linguistics-fail could be loosely defined as shooting yourself in the foot by screwing up a definition, or failure at an attempt to look clever due to incomplete understanding or grasp of the topic.