This word sounds scarier than what it means in 2017, especially in the context of crypto-currencies. An HTTP request to a BTC wallet server in any foreign country could be an 'transfering to an offshore account'. No banks are storing BTC for you AFAIK, no money would be transferred via Swift or other formal means.

And it wouldn't make sense for someone about to go to jail for BTC related crimes to be mailing an encrypted thumb drive to a safe deposit box in a foreign country...

He spent the bitcoins to a new UTXO that the Feds didn't have access to. Since these "accounts" exist on the block chain, which is replicated on computers all over the world, I guess every account is an offshore account.