Crazy stuff you don't know about Alfredo Aceves

A Red Sox columnist who I follow on twitter said today that Aceves has a career record of 21-2.  That didn't seem possible, so I looked it up.  Fact.  In 199 career innings over the past 4 years with the Sox and Yankees he has a 3.21 ERA, a 1.09 WHIP, and a record of 21-2.  Wow.  If those number were all from one season as a starter they would be Cy Young material.  Can he really be that good?  And if he is, why did the Yankees let him go for nothing after last year?  The best explanation I can find comes from Wikipedia, which says he "suffered a broken collarbone in an off-season bicycle accident."  Or maybe they just agree with me on the general principle that middle relievers aren't very good.