I worked at HP during this time helping software vendors port to HP-UX. I also spent some time on the side compiling open source projects for fun on HP-UX and then pushing the required patches back to the project's owner.
Anyone remember Pointcast?! https://en.wikipedia.org/wiki/PointCast_(dotcom)
I was assigned to them briefly.
I think this might be something HP people were telling each other at the time while getting smacked around by Sun. The Sun machines were still ridiculously expensive and while common, I don't think they were the default. SGI Indies were also quite popular and the Pentium Pro quickly started eating the overpriced Unix workstation market. By 2000, I doubt there were that many SV startup developers sitting in front of a Sun box. There were piles of them in server rooms, of course.
This meant that code written on Sun that performed well performed poorly on HP-UX occasionally -- not because HP-UX was a worse platform, but because corner cases in architecture could bite you. On your tier1 development platform you tend to weed those issues out early.
The Sun machines were much more common and a lot of software was tested/built on SunOS.