As a US citizen the answer is always 'yes' even if you lived on the moon.
Or if by some long shot some future president pardons him, he'll be glad he paid his taxes.
I am not a lawyer!
He'll be eligible for the foreign earned income exclusion by filing time. That protects US persons from double taxation up to about $100k of earned income, even without a tax treaty.
And he needs to remember to file his FBARs, too.
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