It is possible. Maybe the peering from his ISP to YouTube is shit/ overloaded. That was an issue for Deutsche Telekom for a few years because Telekom didn’t want to pay for better peering. With a VPN it is possible to get good peering to your ISP and YouTube and in return faster load speeds.
Likely just a network-related issue
Using a VPN on a shitty network won’t magically make your network connection better.
It is possible. Maybe the peering from his ISP to YouTube is shit/ overloaded. That was an issue for Deutsche Telekom for a few years because Telekom didn’t want to pay for better peering. With a VPN it is possible to get good peering to your ISP and YouTube and in return faster load speeds.