Sorry, but how would it know ?
If you mean, how would WIndows know if you've configured a network as metered, isn't that question obvious? Maybe you mean how would I know that it isn't "torrenting" to everyone else on the internet if the connection is metered? The default behavior of Windows 8 and above for the BranchCache services over metered network connections is "block" -- ie to deny the traffic movement over any network link which has the metered flag set. There are actually a number of "sub-flags" available for metered connections that applications can be tuned to leverage, but the simplest of them is "this is a metered connection" and BranchCache will not operate on that link.
There is no reason to believe this behavior has changed with Windows 10, simply because of the public pain it would invoke if the opposite was true. However, also keep in mind that the native WSUS (without torrent abilities) will continue to function over metered connections, but only for what they call "Priority" updates. This too is the default behavior of Windows 8 and above.
Finally, I was wrong about an upstream comment: Microsoft WIndows 8 and above will treat all mobile-broadband adapters as metered connections by default. This means that any onboard cell service in your tablet or laptop that exposes itself as a mobile broadband / dial-on-demand device is considered metered. Also worth noting that ethernet connections cannot be set as a metered device, so if you're using a broadband modem at home and have connected it via ethernet, you should be cognizant that (if left to OS config defaults and if your broadband provider is able to give you service that meets minimum latency and bandwidth requirements) your machine may start offering patches to others.
All things considered, unless you REALLY can't deal with it, I suggest everyone leave the "torrent-like" feature enabled, but restrict it to other PC's on your network rather than "also" over the internet.