Windows does something similar now too. It used to be that USER32 (which owned the windowing system/window manager since Windows 95) would render the wallpaper - but ever since a semi-recent release - either Windows 8 or Windows 10, Explorer.exe became responsible for rendering the wallpaper - and there's definitely some tie-in with the DWM too (you can see this because whenever you kill your session's explorer.exe your desktop wallpaper will disappear). I'm curious what goes on, exactly.