I lost a lot of bitcoin when exchanged closed many years ago. Also I did loose some private keys, because keeping private keys was much more complicated a few years ago.
Most of the friends around me were cheated out of Bitcoin by scammers. When my friend transferred the address, he was familiar with a few letters, so he was not suspicious, and then the coins did not arrive on time before he realized it.
Can you explain more how this scam happened and how much your friend lost?