What's the issue? He bragged about having a bunch of Bitcoin (he does), and left the country and renounced his citizenship.

The US has an exit tax for expats.

While absolutely insane and gross, that's the current tax code. He failed to pay on his Bitcoin cap against on the way out along with other holdings.

He likely lied on his tax returns and didn't pay the required taxes.

I don't follow what the issue is?