It very well could be from drug use but not necessarily cocaine..There are alot of different drugs that people consume threw the nasal passage. Obviously it is something harsh to wreck his nose, I would suggest looking around for some clues..staws,pill bottle the signs are probably there just look for them..Good luck
I think the best question is this...why do you suspect that he's using? Besides the nose, what behavior or actions make you think he's using? Before you answer, I'll tell you that if you think he is..he probably is.