Tyrann Mathieu's personal foul on the 2 pt conversion

Can anyone shed some light on why his hit on Baker was a personal foul?

I saw one step and Mathieu's shoulder to Baker's upper torso.

It feels like yet another BS personal foul call against the Saints.
It was another bad call by NFL Referee's!

Baker was on the outside the tackles acting as if he as going to run with the ball.... he was outside the pocket!
HB took one step and hit him with his shoulder pad after the ball was released...

Should have been considered a clean hit...