Earlier quoted context omitted.
That, plus fanatically good NAT Traversal: https://tailscale.com/blog/how-nat-traversal-works/
But isn't that just part of Wireguard itself? In the end that's what's happening in my case when I exchange data through Wireguard between my flat and the one of my parents... .
The NAT traversal stuff is all magic that happens before the socket is given to wireguard.