He has a ton of NFL coaching experience and worked with very successful coaches like Andy Reid and Harbaugh. Perhaps they vouched for him. He was the Ravens asst head coach so Harbaugh must think a lot of the guy.
No one knows how any of these guys will work out. So many things go into making a successful head coach. Organizational quality and stability is one of the top factors - which, with the Texans, will probably doom him. Like anyone who takes a job with the Lions, Jets, or Jaguars!
I'd rather see a guy like this - who's given decades to coaching in the league - than someone like Urban Meyer who's made his career and millions on the backs of an unlimited supply of free labor in the college ranks.