Is the password matter in this scenario? I will say No as what matters most is your Mnemonic phrase. Besides, it is difficult to forget a password that holds such an amount of BTC if truly it is yours as claimed.
Anything is possible. Maybe he had that wallet for a long time. It's easy to forget when your coins are worth $500 each but much harder when they're $5000 each.
Hate to say it but you can treat it as lost. The only way is if you pick your brain for the typical passwords you like to use. Maybe it's something with your girlfriend or your pet's name. If it's a randomly generated phrase like s1Q2xvy_k! you're fucked.