> "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.
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.