Per the article that’s where he established residency, in order to avoid paying taxes.

Unsurprising. Crypto millionaires retire there too. It's a tax haven thanks to not being a state -- plenty of loopholes you can leverage.

I thought there was an exit tax when you move there

First I've heard of it! I haven't checked the relevant literature in a while. Even so it might still be a net gain for them. Puerto Rico is susceptible to great hurricane tragedies, however (recall Maria.)