One of the features of Windows 10 is to grab updates from other Win10 machines on the same local subnet in P2P mode; the idea on not saturating the WAN link to the ISP with redundant requests. Problem is, I don't think I've ever seen it work. And yes, I only had two Win10 machines on the same network with one already updated. It's network utilization remained at 0% while the other computer was updating. that said even if this function is supposed to work as it is I'm not even sure how differential updating will work in a P2P environment.
I don't think I've ever seen this work either. It would be damn useful - but I've never seen or heard anyone else getting it working either.