Xbox One disconnected from the internet -problem
It's actually a fairly common problem with xbox live that dates right back to the 360. I doubt the other player has caused any damage or that he even could. NAT issues occur with how your router works, but its a pretty blanket statement for xbox live connectivity issues.
http://support.xbox.com/en-GB/xbox-360/networking/nat-error-solution
Most of the time its down to uPnP (universal plug and play), especially your xbox tells the router what it needs to do to connect to XBL, however the two do not always interact smoothly resulting in temporary connectivity issues.