The deep post isn't covered. The receiver has leverage on the DB and if the ball is thrown just in front of him has the angle to beat the defender to the corner for 6.
#28 is the read. If he stays on the post throw the sideline. If he plays the sideline throw the post. You can miss on the throw there but you cannot miss on the read. That is QB101. Brady has designed a shot play with a single defender read. On that play it was good coordinating. Bad Quarterbacking.