I can't speak to the injury you're referring to, but if the Bills didn't report it and the league didn't punish them for failure to do so then it probably wasn't you think it was..
"With the practice report, all players who have reportable injuries must be listed here, even if the player takes all the reps in practice, and even if the team is certain that he will play in the upcoming game."
So there's two possibilities I guess
1. It wasn't a reportable injury (which what a 'reportable' injury is pretty vague). There's all kind of crazy rules like some injuries have to be reported for 'key' players or player that would have increased media interest, but wouldn't have to be reported for you 3rd running back who may or may not be active.
2. They don't have to report it every single day. It's 3 days before the game for the practice report and a game status report 1-2 days before the game(depending on the day they play)