Although he was formerly Head Coach of the Dallas Cowboys (1998-1999) and Offensive Coordinator for the Miami Dolphins in 2000-2001, as well as WR Coach (1994-96) in Pittsburgh and OC there (1996-97) as well in KC (2008) and an Assistant Coach and eventually OC in Denver in the 1980s, he doesn't belong to any specific NFL "coaching tree". He was also notably the HC for Georgia Tech (2002-2007) too. What all this means is that he made it on his own merit, not on the basis of anyone specific he had previously worked for or had a relationship with. In other words, he is where he is on the basis of his own brain power and what he's been able to achieve on his own. I like and respect that.
I also like the fact that Dave Wannstedt, the new DC, is a member of the Jimmy Johnson coaching tree, which I like better than most NFL coaching trees. I hope he works well in Buffalo under Chan.