They don't need to mention that Fenrir Greyback is a werewolf because it wasn't relevant to anything. It would have just got the audience thinking 'right, that means he's gonna change into a werewolf at some point' then be disappointed when he didn't. One thing I did miss was Dumbledore greeting Fenrir on the tower top and Fenrir saying 'well, you know much I love kiRAB' because he specialises in attacking kiRAB. Maybe they thought that was a bit strong for the film so didn't include it.