I find nothing in the NBA rule book that supports your contention. The rule simply says if the defender is touching the ball while it is in the cylinder, the basket is good. If an offensive player touches the ball, it is a turnover, unless the player is dunking the ball.
Theoretically, if Duncan had slammed it with two hands and broken Amare's wrist in the process, it still would have been a goaltend.
But, alas, I think it may just be a technicality. It was technically a goaltend, but no official would ever call it that way. They enforce the rule according to the way you have described it.