I'm sure it is, but last year was the exception for him. He is throwing the ball this year just like he did almost every single year in his career before last year and no his BABIP is not just coming from mechanical issues, its almost certainly not sustainable given just how low it is this year. Last year I'm sure his mechanics were off its why his stats were so far outside the norm and screamed regression back to his previous 3 year average, which is exactly what happened. That is dependent on the line drives he allows, more times than not he's going to be a lower BABIP, avg. HRs allowed, lower H/9, and low Ks will generate lower BABIP as I'm sure you know. But, what causes low BABIP for sinkerballers is movement on the two seamer not hitting the sweet spot of the bat, it's nice when they're past the trademark. If he can keep everything in line as far as his glove arm, balance, and stride leg positioning to stay closed and not deviate for the plan of attack, I think he could maintain or surpass his current BABIP despite it being espec. low. I believe the pitcher much like hitters (not so much hitters b/c of HRs and Ks and apporach at the plate) can dictate their BABIP by how well they hit line drives or for the pitchers how well they prevent line drives.