hello i appreciate you are looking out for your friend but this needs medical attention.
We are not doctors but on research could be anything from twisted testicle to a cyst and any lumps should be reported.
My advise to your friend is get checked out and especially to rule out any cancerous lumps.
My nephew of 21 had this and it turned out to be a minor ailment so don,t be scared by this answer as its common sense to seek medical help with any testicular lumps.
good luck.