Hello,welcome to HCM,
thanks for your query.from the experience at my clinic ;
1. unaccustomed heavy lifting does cause some damage. in this case it is mostly intact muscle belly separated from its bunch or a bursa which has bulged out.Bursa is a fluid filled sack close to joints to help in smooth movement.
2. the above two things may remain as they are /may not go back to their original position.not to worry.
3.he can take painkiller+muscle relaxant(diclofenac+chlorsoxazone) to reduce pain/swelling for a couple of days.
4.another rare possibility is a previous enlarged lymph node
which came to notice at that time.if associated fever
,weakness etc. are present ,can visit physician.
happy to help.