Could a very minor hit to the testis cause epidymits orchitis?

No,... A hit at most means a contusion, which results in tissue bruise, and in turn, it will heal up without consequence. For a man of 39, i would still concern about possible std-related epididymitis if any. So, collect the feature-degree and progress of pain over time, and bring those to see doc timely for analysis, physicals, possible tests... So to deduce DX for proposing rx. Best wish...