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.
Using a VPN on a shitty network won’t magically make your network connection better.
No, but it does affect what route your traffic goes through.
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.