He might experience the same thing because that device is infected and his clipboard is already hijacked.
I think blockchain seed is compatible with Electrum BIP39 enabled try to suggest it to him.
He'll experience worse especially if during the sweep process he imports the keys or seed with his clipboard. Best thing to do is to format the affected device. Sometimes you can't really be certain it's it's a clipboard virus or a keylogger and trust me keyloggers are far worse.
We are going to create a new wallet on hardware device, to create an address, then we will import his current wallet to the hardware device, and send those coins to the newly created wallet...... So we are taking precautions. I told him he needs to secure his mnemonic phrase immediately, then after the coins have been secured, wipe and re-install his operating system.
Depending on how much coins he has he can set up a cold wallet for better safety. He can use a watch only wallet to create the transaction and sign it in the cold wallet then broadcast in the hot wallet.
That aside. He should be careful the sites he visits and permissions he grants to softwares get installs.