How much of the credit for low shots against can actually be given to the defense coach?
It's hard to say. Bill Peters ran a system that had the defensemen aggressively pinching and playing very tight gaps in the neutral zone. It led to very strong possession, but also had little room for error when it broke down. That, IMO, was the biggest reason for the shot suppression numbers for Carolina. That said, Smith had to be able to coach his guys in a way to execute the plan and he seemed to do that. Canes also had an excellent PK for a couple years under him.
Last year was a disappointment on the defensive front. The PK wasn't very good and many of the defensemen seemed to really underperform. They weren't as good on ice as you would expect them to be on paper. Having Darling in net was a factor. And it was reported that the team tuned out Peters by the end of the season so it's hard to say what contribution Smith had to that, but it was disappointing none-the-less.
Was honestly surprised that he didn't quit/get fired right away after Peters was gone and Brindy was named head coach. He was brought in under Francis/Peters and to once his "peer" get the head coaching job, I thought he'd be gone. Maybe he was looking and waiting it out until he had something lined up? (speculating).
I think he's a good fit for the Sabres though and you will probably be pretty happy with him.