Or 3) He wants his future to be in the NFL as an OC and/or head coach and thinks (right or wrong) that the best path to that goal is to get back to the NFL as a QB coach.
My guess is that he is young and confident enough that he assumes that he'll make back whatever he leaves on the table here in short order if his career folows the path he thinks it will.
I think you're right. Fisch seems to be an NFL guy, might not have been comfortable with the college game, amateur athletes, etc., and wants to get back to more familiar territory.