No, AU/X was far from the first OS Apple had for Mac. You needed a big "mac II" or bettr to run it. It was not popular and as I remember it was expensive. It's really to bad they did not continue it. We would have has Mac OS X a decade earlier.
I have two "512K Macs" with software in my attic. These were very close to the first Macs. There is no way those little machines could run UNIX.