Stress fracture shouldn't have kept him away this long as it was. The shut-down was more of a "we're not going to sacrifice your health even if we make the playoffs" type of deal, so he probably is better than expected for them to entertain this notion, from both a injury perspective and/or from a body shape perspective.
But that he's back from a stress fracture right now shouldn't be a surprise. The decision to shut him down for the season had little to do with the time table in which this type of injury takes to heal.