They were; their main point of connection was at the OS level, as Accent on PERQ begat Mach, and Andrew originally ran atop CMU’s Mach+BSD environment (MK+UX). That let it take advantage of features such as Mach IPC and dynamic loading of shared libraries and plug-in modules. Later Andrew was ported to vendor operating systems, and then to run atop X11 instead of wm.