Convey congrats to him
If it is a real approval, he will get FP notice along with his approval Notice because FP is a formality to be done before stamping and ofcourse approval. Or while checking AVM, he would have entered the EAC number of EAD and got confused by hearing "This case has been approved".
This may be possible as it happens before in CSC for most who applied between Feb to may 2001 got their approvals within 4 months from RD and even have their GC actual card in their hands.