I wasn't surprised. The Chargers were blown out the previous game and their head coach fired. They had ten days to think it over and get behind the interim coach, who by all accounts is a players' coach who rallied the team. They were ready to give it their best shot. Meanwhile, the Bills were coming off a short week and had to fly cross country, so not surprised they were a bit flat. Put those together and you have the game that happened. I think the game actually showed us something about this Bills team. They easily could have lost with those dynamics, and they didn't. They took care of business.
I suspect something similar will happen tomorrow night. Like the Chargers, the Dolphins were embarrassed the week before, and they're playing at home, down on their luck and counted out. That's a formula for some fight--at least for some teams. The Bills will be ready, though, or at least I think so. They've been hard to figure out this year, even in retrospect.