I don't think it is that surprising. The guy probably sees himself as a NFL coach and if he has a chance to make the jump to the pro game, he has to start somewhere.
Last year Jim Reid resigned as the Virginia Military Institute's head coach to become our Inside Linebackers coach. Steve Bush resigned as a high school head coach to become our Offensive Quality Control coach.
Even though these guys left head coaching jobs for, lets be honest, hardly glamorous NFL jobs, it is a good step in their coaching careers. It is probably easier to become a future NFL coordinator if you have NFL experience and not coaching a high school team or a lower level football college.