It was 5.3 which varied from 5.2 due to the 386ix extensions. I used it when it was owned by Kodak. It was indeed bought by Sun and it became the base for Solaris. The original Sun OS was BSD based and was the basis for their original servers. Both were true Unix, unless you want to argue that AT&T variants are more/less uxix than Berkley, which I would consider pointless.
The only reason I remember this is because my first real unix project was a protocol converter/terminal emulator for Honeywell DPS 6/7/8 mini's to run on 386ix Unix. We sub-contracted to Sun who was sub-contracted to Martin-Marrietta and we also sub-contracted to a bunch called C3. C3 specified a Zenith 386 box with Interactive unix, and Sun made a special 386ix box they called the Roadrunner which ran a version of their BSD based OS. The end user was Military Airlift Command. I got my stuff working well on both, but Honeywell Federal Systems also proposed a Mac with their own pc/te on it and threatened to have shortages of parts for DPS 6's if MAC didn't use their product. Two years later, Honey Federal Systems called up my boss and inquired if I could get communications running on their Macintosh. I declined, somewhat less politely than usual.