No, that's actually my real and only Xorg, it's the child process of /usr/libexec/gdm-x-session and that process is owned by my real user id, and the Xorg process provides /tmp/.X11-unix/X1 that e.g. strace -e connect xlsclients shows is the socket it uses. Notice also that it uses a significant amount of memory and has consumed a meaningful amount of CPU time, much more than a dm would do.
Good point about display manager though, I suppose it's not using Xorg then as I do know there is a login screen waiting at vt1 but that's the only Xorg process. Maybe the gdm3 incorporates a Wayland implementation in Debian 13.