Many people do not know this as it is not a clear and well documented feature, but by default Windows 10 uses your internet connection to distribute Windows Updates to other users. I'm guessing they use the same sort of concept as a bittorrent network. The way Windows 10 is setup to distribute updates using your connection without asking can cause problems with you lagging or going over a data cap limit if your ISP has a cap.
You can change the settings to either completely disable distribution of updates, or you can allow it to only distribute updates to other computers on your local network. Personally, I allow computers on my local network since my computer is always on and it can instantly provide updates to the other computers in my house when they are turned on.
Here is an excellent and detailed article from pcworld that walks you through the process of changing the update settings:
http://www.pcworld.com/article/2955491/w...stems.html