I haven't heard anyone mention this, however this is the only reason I could think of that would (maybe) make the punt a good idea...
It's 4th and 1 at the 40. A punt will push the ball 30 yards down the field to the 10. There is not much time left and the Colts sucks, so was McD thinking that the Colts were in 4 down territory? The hope may have been that the Bills gain 30 yards in field position and 4 plays later have the ball deep in Colts territory when the Colts fail to get the 1st on 4th and whatever.