I'm not familiar with qtile, but I'm fairly sure there's currently no way to get information about the active window on mutter unfortunately.
Thing with wayland is, each compositor has to implement things their own way, so you're limited to what your compositor allows you to do.
For instance, you can get window information in sway with swaymsg. On other compositors you may have to find workarounds.
Wow, I wish I knew this workaround during my early gameplay lol.