> "why exactly are they showing up at a donors gathering?"
Yes, this probably means the problem is even bigger than the sample demonstrates. Most of the people in uncomfortable retirement are not going to show up at all.
I wouldn't be that inclined to make assumptions about what sort of selection bias there was. I could also argue that people who show up at such gatherings are more likely to be people with time on their hands or who are making a concerted effort to network, while those who are working full-time are busier.