I agree on that as far as trying the solution. I closed off the stop valve by a toilet of mine also to stop a toilet from making so much noise after replacing the ballcock with a different one. The new ballcock probably was more restricted but I also know that the gate inside the stop valve may wash and never close right in the future but I'll just replace it later.
If this guys problem is not the toilet then he shouldn't adjust the valve at the meter or just inside the house. Those should be saved for emergency shutoff as either one could go bad at anytime(I've seen them both leak and fixing plumbing when that happens isn't fun)(because of that I recommend that someone doing any plumbing on their house that has a gate valve just inside the house to add a new ball valve with a bleeder as a backup next to it). I suspect something just happened recently to a valve in his house. He probably should have a plumber look at it if we don't get it for him.