Reading between the lines here (and as someone who has had the "pleasure" of applying for US visas) I get the strong sense that his attitude/arrogance was behind his rejection.

You have to attend an interview for a US travel visa (or almost all visas except under the VWP) they'll ask you a bunch of questions about your trip, and then ask you about your life in your home country (e.g. do you have a job? family? etc) to see if you have a reason to return (ties).

I bet he turned up to the interview, spouted off about being a former US citizen, expecting to get a free ride, pretending like the rules don't apply, and is likely "unemployed" in his current home country (since he is living off of wealth). So they of course stamped him rejected because he really is tied to no particular country, and was likely quite adversarial when questioned.

I mean the t-shirt alone (and self-describing as libertarian) suggests to me that this individual isn't well suited to the slow annoying process that is US immigration (it is like pulling nails). And unfortunately for him now he isn't a citizen they get to treat him like everyone else (no special treatment).

I think the US international tax policies are insane. But I think US citizens who give up their citizenship and then whine when they get treated like every other foreigner can piss off. You cannot have your cake and eat it too. Heck, why not use your wealth to lobby the USG to reform the tax rules?