I disagree slightly. If the general population doesn't know or care about the Bills - they're likely not to bet. The people that will bet are the professionals that see a winner (either way) or the fans of that said team. In the end - Vegas does care about the Bills and put the line where it is for a reason. They know the norms of the bettor and who bets.
My guess is they set it at 6.5 - know the majority of Bills bets will come from fans of the team and that they'll bet the over. Again, my guess is, they see us winning less than 7 games.