In those 31 innings, Gray totaled 23 strikeouts and allowed just five walks. His strikeouts per nine innings rate could be higher, but that's solid control.
And it's a skill he's demonstrated throughout his career. The highest walk rates he's ever posted came in 2007 and 2008, in Triple A both times, and were barely above 3.00. And when Gray went back down to Triple A in 2009, he only walked six batters in 41 innings.
The kid's got good stuff, too. His average fastball velocity clocks in around 94mph, and he's also got a slider, curve, and change in his repertoire.
From the limited sample available, Gray's numbers make it seem like he stands a decent chance of contributing to the major league club's bullpen once his groin strain heals up. Apparently that might take a while, though? Oh well.