As you said, it was 2-0. He probably wasn't thinking sinker. He probably thought he got a fat one and he thought wrong. Not many pitchers have the huevos to throw sinker on 2-0. The fact that he shattered his bat tells me it went off the end of the bat. That = Great Pitch.
sinker = his fastball. That's all Johnson throws. Of course he is going to throw his best pitch on a 2-0 count. Mid 90s sinking fastball.