If they were going to completely give up anything related to their career then yes but that wasn't what was described in the post - nor do I think retirement these days tends to mean "stop working". I think we're mostly past that notion since quite a few people live so long and desire fulfillment through jobs. (And jobs don't break your body as frequently as they used to)
After interacting with some people with FU money, they don't tend to give up on career very easily. They don't want to be stuck at home - they want to keep doing stuff. So, inevitably, they keep working, doing startups, taking on executive roles at big companies after they realize they suck at startups (like most people - obviously)... because that's what they know best and feel most useful for. From the people I know, once someone whose identity relies on being a provider suddenly no longer has to work to provide... they tend to have a bit low of satisfaction unless they keep working. So they work even though they don't need to because it gives them a bit more purpose/happiness/whatever.