I don't think he threw hard in college. He just had incredible control or at least the ability to throw strikes. 18 walks in 376 innings would be hard to accomplish even with Eric Gregg doing his "wide" strike zone. His dominance would lead me to think he had a good mix and command of the pitchers. With the Orioles I don't remember him throwing more than 86. Greinke now works mostly at 88 but can still put a 92 in when he wants but he just pitches and pitches.
A comparable would have been George Kirby at Elon walking 6 in 88 innings his Junior year, but he would still throw 92 in the seventh inning. I here he is now 97 in the camps last year. They rarely have the big inning due to walks. Then there is Bartolo Colon throwing nothing but fastballs at 90 and having good success hitting corners at age 43 or whatever it may have actually been.