Kmet initiated the contact to drive the defender away from the boundary to give his QB a spot to throw the ball in the back of the end zone. Smart play. Not sure the exact rules, all I know is if a defender imitates any contact after 5 yards they can be called for illegal contact
So that explains why Durant ran away from the ballbon the game-tying TD...
If this isn't OPI I'm not sure what is 😅