Are you sure the passphrase wasn't the password of his encrypted wallet file instead? What your script is doing, it's to use the passphrases as private keys of adresses hashed with SHA256. So it's a brainwallet basically. But if it was so "simple" I guess your friend would have already tried it with one tool or another during those 10 passed years, especially with the exponential increasing price of BTC, don't you think? Anyway I hope you will be able to find more clues. May Santa Claus be generous with you.
I do not know how in 2014 mining worked in the sense, wallet and mining to the btc address happened at the same time?
It was transparent to the miner? Not sure.
From what he told, he used a password or passphrase which then lead to a BTC address and than mined to that address.
He does not have a wallet file.