Hi ! The history of injury
to the scrotum
suggests that there could be some collection of blood in the scrotum due to trauma to testes. The extra flabby skin which is noted by you may be a subcutaneous deposit of blood. I wonder if he does have any pain or not. If what has been just told is correct, I would suggest you to consult a urologist
at the earliest, as the trauma caused to the testes may prove to be serious if not dealt with urgently. If possible, go to him with a ready ultrasound
report. Please take care.