To reassure you, if a board certified ENT doctor evaluated your nostril
and felt your concern was cartilage
, it is highly unlikely to be anything else.
It is common to see asymmetric cartilage bulges, bends, folds, etc. within the nostrils. It would be especially unlikely to be confused with a tumor. I only recommend that If you feel the site changes at all in the future, have it re-checked.