For what it's worth, here's what he said after the game:
"You never want to hit anybody in the face. It's not easy to pitch after you do that. I was trying to go inside there and it just sailed on me. I definitely feel bad about it. It was not easy to stay out there and re-concentrate."
He said the right things, and I don't see much reason to doubt that he was being genuine. In the context in which it happened, you gotta feel for deGrom too. He's now got the bases loaded and one out in a tie game. He's in some serious trouble. Sure enough, he gave up two crucial runs that inning which essentially decided the game. I think there's actually something kind of stoic and admirable about keeping yourself composed and trying to stay in the moment, do your job, get through the inning. I'm sure he had plenty of time to feel bad later, reach out to Mitch, all that.
Besides, what I saw in-game looked more like shock than nonchalance. I think he just wasn't sure how to process it, and knew that he needed to try to stay focused and survive the inning before he checked in with his emotional self.
Just my 0.02 cents as an armchair psychologist. The sports fan in me doesn't see any reason to harbor a grudge about today's incident. But I totally agree about how wrong it is to throw at a guy's head with malice aforethought. Who was it last year, Ianetta maybe, who got lit up by Matt Bush of the Rangers (fresh out of jail no less) in the first couple weeks of the season. I lost all respect for Jeff Banister that day, for the way he reacted to what was some pretty blatant head-hunting by his pitcher. The Rangers coaches all stormed out of the dugout like they wanted a fight, even though it was their guy who threw the sucker punch. I remember Blowers muttering "bush league" in the booth as it unfolded.