First things first: yes, that's grass he was eating. He left no doubt about that. However, his remarks, captured by reporter Katherine Terrell, do leave other things in doubt. Like Miles' sanity (and we mean that in a good way, if that makes sense):
"(Synthetic turf) is not nearly as tasty. ... I played baseball when I was a young man, I played football, and I always seemed to enjoy a blade or two every now and then. Not that it was a meal in any way. ... As a kid I'd have some and leave it there for a while. ... Traditionally I'll put my knee on the ground and look for a blade now and then."
Emphasis ours. Certainly the best part of that explanation is Miles clarifying that no, the grass he ate did not provide sufficient nourishment to constitute an entire meal. (We are grateful for this clarification.) We also enjoy that he describes the habit so casually - hey, eating grass is second nature to the guy.
You can also view Miles discussing his grass-eating further (in remarks separate from the ones block quoted here). About the only thing we're sure of after reading/watching all this: Mike Leach's dismissal at Texas Tech clearly didn't rob us of all the great characters in college football.