How does Windows 10 select among DNS servers on multiple adapters?

I've been seeing an issue recently with VPN users who can't properly resolve our internal addresses.

As near as I can tell, the machine used the local network to resolve DNS, and some ISPs DNS servers, instead of responding 'I don't know' to unknown address requests, return some useless IP for 'dnserrorassist.att.net' or whatever (which--omgwtf!?).

So far I've solved this by forcing local DNS to use 8.8.8.8, but I found an article recently that suggests simply changing the route metric for the VPN to be lower than the local adapter. I realized that I have a deeper problem: I don't understand how Windows name resolution actually works. It seems obvious that it chooses the DNS server on the lower-metric adapter and then falls back to another, but I've never actually seen this written down anywhere (and it's been more than a few years since I did networking 101).

Can someone explain this or point me to an article for it? Thanks!