There are a lot of fans who just do not understand what PI is. When that play happened and even after the replay I knew that by the rules as written Watkins was not guilt of PI. He was clearly a half step ahead of the receiver and was clearly playing the ball and not the receiver, if anyone was going to catch that pass it was Watkins not the receiver.
Another thing that is puzzling to me is all those fans who complain that the Cowboys secondary isn't aggressive enough, Well hello that is what aggressive coverage looks like in todays NFL. You can't bump and run aggressively any more but you can make a aggressive move while playing for the interception. That is the only time after the 5 yard zone which aggressive contact is allowed, so you bump them off the LOS and you make plays on the ball when it is delivered. That is todays NFL.
It is a judgment call so it could have been called PI but in this instance it was called correctly and was a great play by Watkins.