To piggyback off of what zzzmanwitz said, yes, FIP,WAR, etc. do a very good job of telling us what to expect going forward. However, the other function of these stats is that they do a good job of isolating events on the baseball field and telling us how well a pitcher performed on the stuff he could control. Greinke has done well for the most part on the stuff he can control (K's, BBs). His LD% is higher than usual, and he has given up quite a few HR/FB. So while he hasn't been perfect with what he controls, Greinke has done pretty well overall. The stuff that he doesn't control (LOB%, BABIP) have been unsustainably below average, causing his ERA and "results" to appear poor. However, this doesn't mean that Greinke has been pitching poorly. It means that he has been pitching well in general, but he has run into bad luck, defense, etc.