Weston is the reference implementation of Wayland, but it is not the only one - KDE's KWin is another.
Xorg is the current most common implementation of the X11 protocol, however - again - it is not the only one (although almost all Linux desktop systems today use it) and there are other implementations.
So how do X11 and Wayland relate to each other? Well, they are both protocols for providing a windowing system. They each do things differently, with pros and cons to each approach. They are different enough so that one can be implemented on top of the other, so compatibility should not be a problem, although obviously features are lost or crippled when doing so.
There is this misconception that Wayland obsoletes X11, but they are very different systems designed by different people and worked by (mostly) different developers that only superficially provide the same features (showing windows on screen) that - at least personally - i do not see that happenning any time soon, if ever. Personally the way i see it is similar to asking if Atom (or VSCode, if that is your poison) obsoletes Emacs (or Vim).