You mean concentrating on the secondary by spending the biggest resources trading for a DT, signing a DT, signing a LB, and drafting CB, WR, DE?
Look, I agree it was a huge mistake for the Bills to not sign a veteran offensive linemen or two. It would have been ideal to sign someone like a Wesley Britt, LJ Shelton, or Anthony Clement for some depth at tackle.
Saying they "concentrated on the secondary" is a bit of a stretch when you're talking about their off-season. Especially since no one drafted after round 3 would have mattered this year depth-wise anyway.