Watch the film, he turned his shoulder. Not much, but he turned his shoulder. Any time you pull someone while they're running, its going to get them off stride. Plus, if you're running behind someone, not making a play on the ball, and you trip them, it is pass interference, it doesn't matter if it's incidental or not. He was not making a play on the ball, so he can not touch him at all.
On the Harris play, you're probably right, I was in the can on that play. I saw part of the replay on that. Was it reviewed? I don't know if there was a good enough angle to overturn it, though.