No, it was not grazing. He swiped down with his hand and made solid contact that obstructed Lebron's motion. Easy call and obvious because the swiping down brought attention to the act.
I agree that the grazing fouls are regularly ignored, such as one Pierce had on a Lebron jumper, but Pierce merely raise his hand up for the block. Pietrus swiped and made solid contact on Lebron's arm. Good call by the refs on that one.
My problem isn't whether there was contact or not, I actually admit there was contact on that play. But, again, there is contact (illegal contact, at that) on tons and tons of shots in the NBA. The obvious ones usually get called and you hope the unobvious ones get called a fair amount on both sides of the court.
My problem is when the foul was called. It wasn't until the ref noticed that it was an airball that the foul was called. If the shot went in, do you honestly believe the whistle would have been called? Because the whistle was clearly blown after the result of the shot was known. That is a bail out call for a superstar.