After a dragon attack on Raven Rock, Mogrul and Slitter are hostile towards me. It's pretty unlikely that I hit them by accident though. Mogrul is immortal and the guards are joining the fight on my side, so I think this isn't supposed to happen. I've started no quest related to Mogrul so far.

Try leaving the area and commit a small crime in another part of the hold. pay off the fine and there hostility towards you should stop

Thank you, it actually worked.