So… does it follow that the very wealthy basically hold a massive IOU to the general public?

To expand the sibling comment. In principle the money would reflect IOUs the general public owes them. But also following this logic the way I see it is they accumulated their money was by getting more IOUs through: people employment (being able to command a big pool of work and get a cut of IOUs from it), arbitrage (exchanging lower value IOUs with higher value IOUs), or simply stealing (eg. siphoning government resources).

If by wealthy you mean people with a lot of money specifically, than no, the IOU is the other way around.

They hold IOUs from the general public.