The inheritance sounds a bit informal, but
IF the aunt was the executor
AND she distributed the gun according to the decedent's wishes
THEN it sounds like it really was an inheritance.
In the colloquial sense yes, but legally that sounds a bit questionable. Verbal contracts are pretty sketchy in most places if accepted at all legally. To assume it was legally an inheritance puts the OP in a serious bind if the federal government and/or the state of California do not agree that a verbal request counts legally as a bequest.