"A player may continue to move after gaining a guarding position in the path of an opponent provided he is not moving directly or obliquely toward his opponent when contact occurs."

That quote directly from the rule book proves the two former NBA coaches have no idea what they are talking about. They both said it was a block because Green's feet weren't set. It doesn't matter if a defender's feet are set or not when are the primary defender on the ball and beat the offensive player to the spot.