How was this possible, for the change to be sent to a new address? If I understand correctly what you're saying is that the account was split in two: one part went to the wanted destination and the rest to an unwanted destination.
Yes, this is how Bitcoin is designed and has worked from the beginning. The problem is his wallet did save the private key for the change address he just didn’t save the wallet, so it was lost - the changed address wasn’t unwanted, it was wanted, it just didn’t get saved. I believe early Bitcoin wallets generated addresses randomly so you couldn’t recover everything from a seed and had to save your wallet.
