I have ferrets - 8 of them at the moment and up to 15 at one time over the years. Usually they do not bite and seldom even get scared. However, it does happen and sometimes a ferret will bite. And a nose would be just the right size.... and the poor ferret probably had his tooth stuck - hence the "gnawing" part as he/she was trying to escape the thing that had him.
I have seen people who are "ferret experts" get bit on the nose by a new/strange ferret that is utterly terrified of the stranger trying to pry open his mouth or turn him upside down. It's never a pretty picture.