The Dolphins wouldn't have been able to block Foerster from interviewing for a head coaching position, so that is where the rule is tricky to some but that wasn't the case in this instance. I know PFF came out with their grades recently and Miami was rated the 3rd worst offensive line in 2016 which is a bunch of hogwash if you ask me. That is a case of a statistic or ranking not telling the entire story. When healthy Miami has a top five offensive line in the league and they played like it when they were healthy. Foerster does deserve some credit for how this unit has played considering someone like Jermon Bushrod a career left tackle moved to right guard and played well this past season in a new position. Also Laremy Tunsil someone who has never played guard before moved to left guard and was better than expected in that role.
It's unfortunate for Foerster that he won't be able to interview for a position like offensive coordinator but it's very good for Miami to be able to hold onto a very good coach.
UPDATE: The Denver Broncos have hired Jeff Davidson away from San Diego to be their new offensive line coach. Looks like Washburn will be staying in Miami for now.