I do wonder (as this was something that did occur from time to time in my own playing days) if there was some culmination of verbal warnings by the official regarding WR contact with the DB during the game, which led to an eventual penalty. It is not unusual for either lobbying to lead to a foul, or a ref proactively telling a player to knock it off, and frankly letting it slide no more. Of course, one would have to watch all of Davis' routes, or learn of the sideline banter.