It's never been confirmed 100% that Quartz Composer is a descendant of PixelShox, but this is widely believed to be true.
As you mention, the creator of PixelShox had to stop developing the software after he took a full-time position in the computer graphics field. Those familiar with PixelShox have also noted the uncanny similarity between the Composer apps of the two systems. The hardware-accelerated aspects of Quartz are extremely similar to the sorts of things which PixelShox advertised. Most interesting of all is that the creator hoped to expand upon PixelShox, which was originally touted as cross-platform... even though he only got the Mac version working.
It looks like a duck, walks like a duck, and quacks like a duck. There's a pretty good chance that it's a duck.