This was unprecedented. Here is a list of the 20 pitchers in baseball who had more than 10 K's per 9 while walking less than 2 per 9. None of them had ERA's higher than 3.23.
A .350 BABIP and Left On Base % in the mid 50's was the culprit. That bad luck couldn't hold up, course, and Greinke ended the season with a much more respectable .318 BABIP and 70% LOB while continuing to strike out over a batter per inning and walk next to no one. His unlucky May and June hurt his overall ERA but his defense (and luck) independent statistics show him as a pitcher who should have had an ERA closer to 3 than 4.