Yes, it is wrong as many commenters on the site also point out. He could have multiple backups of his wallet file and spending the bitcoins out of one of his backups would invalidate the coins in the wallet the FBI has.
If he stored the bitcoins in a single address, and he has the private key stashed somewhere, then even if the wallet file is deleted, it can be retrieved. This is how bitcoin works, if you have the ECDSA private key of a bitcoin address, you can spend those bitcoins without having the need for a wallet :)