I don't think that was below the knees. His shoulder pad hits Jaren's thigh
right above the knee. I guess I don't know all the rules and a roughing the passer penalty was called, so no sense in me trying to double down on my bad opinion, especially when I'm getting roasted for it in the thumbs down category.
But you can see the play in full speed in this video below at the 22:20 mark. If it's considered dirty for a defender to dive into the thighs of quarterback while in mid pass, then I guess that's a dirty play.