It seems like most people are assuming this was a polite way of firing him. If I had to guess I think the Bills and McBeane are being sincere in that it was Frazier's decision and they weren't the ones that wanted to move on. If they wanted to show him respect they wouldn't have waited until all the other coordinator jobs around the league were filled.
Regardless, he's gone, and that's exciting, even though it's unlikely things change much.