Sure, sometimes people get social engineered into taking money from their bank account and giving it to criminals. Should banks stop allowing withdrawals?
I disagree with him. While yes, it's awful and tragic that happened to his grandmother, I think it's incredibly dangerous to allow companies to lock down our devices like that. And I think from a practical perspective, we're never going to be able to eliminate these attack vectors fully; if the grandmother was going to go along with this scammer in this particular way, there would always be some vector that she would fall for, no matter how hard we might try to lock them down.
But I can't bring myself to say his stance is unreasonable. He's dealing with a devastated family member whose retirement is now ruined, and he has to help her pick up the pieces. Not a good position to be in.