If the Bills lose the game against Miami and need a Wildcard spot with a 10-7 record, you are correct about the Browns.
In the 10-7 Bills Wildcard scenario, what people are not seeing is the Bills want the Browns to win and take Seed #5.
The Bills will not get the 5th seed.
Where it gets tricky is finding who needs to win and lose for the Bills to get one of the remaining seeds.
That will be clearer after this week's games.