I agree. The ypg were low because the other teams ran all day on the league's worst run defense. The opposition threw against the Bills only 473 times all season, the 2nd lowest number of attempts against in the league, and they were run on 571 times, the most of any team in the league by a pretty substantial amount.
If you look at other pass defense statistics you can see that the Bills aren't that great. Opposing QB's had a collective passer rating of 92.6, 5th highest in the league. The defense allowed a TD on 5.9% of the passes thrown against them, 4th highest in the league, and they gave up 28 TD, 7th most in the league. They had only 11 INT, 4th fewest in the league, and they only intercepted 2.3% of the passes thrown against them, tied for 6th lowest in the league.
It's all here: http://www.pro-football-reference.com/years/2010/opp.htm
The Bills' pass defense is ok, but not elite.