There's a hefty exit tax, around 50%. Not like many other non US countries. He may not have done it the right and or legal way.
I don’t like this guy, but make it make sense that someone who renounced their US citizenship in 2014 can be charged for tax evasion in 2017?
https://decrypt.co/330431/bitcoin-jesus-ver-sues-spain-block-extradition-us-tax-charges
Discussion
I could see that being the case with him, but it’s still crap.