Offensive pass interference is "cutting off the path of an opponent by making contact with him, without playing the ball."
You have to look like you are running a route and any contact is purely happenstance. It requires acting. Also, you usually aren't looking to hit the defender, just merely make them run around you and lose a step or two.
"Blocking more than one yard beyond the line of scrimmage by an offensive player prior to a pass being thrown is offensive pass interference."
Illegal pick plays only count if they are 1 yard beyond the line of scrimmage. Otherwise, it is considered legal blocking.