Anything can happen in the NFL, but the Browns have a lot to overcome, starting with the strength of that division. The Bills were able to take advantage of beating a very bad Miami team twice (the Dolphins were 4-12 and 2-10 inside the AFC) and going 4-0 against a very bad NFC West (the teams were a combined 25-39, 3-10 against the AFC, and the division winner, Seattle, was slightly better than 500 and actually outscored by its opponents, albeit by only two points).
Looking at it another way, Buffalo feasted off six opponents with a combined record of 33-63 (doubling Miami)... or on average, 5.5 wins 10.5 losses.
Granted, the Bills had to win those games, but by NFL standards, that was about as favorable as a schedule gets. In other games, Buffalo was 3-7.
As has been pointed out, the Browns have a much more difficult hill to climb. They could be significantly better and struggle to win more than a game or two inside their division. They have some very difficult non-division games.
It's foolish to predict that any NFL team will be bad, given recent history, but the advantages that helped other teams struggle from worst to first, or whatever, don't appear to be in place for the Browns. They have the look of a team that will struggle to win many games, even if improved from last season.