twostep - being an accountant, I'm used to people sometimes speaking (or writing) in haste and confusing the technicalities of a transaction. The point is that the US tax is based on an amount of money (in dollars) that he never saw. Basically, he's being taxed on paper profits - and what's worse, because he immediately re-invested the money in Germany, he has to dig into his own pocket in US dollars to pay the taxes to the IRS.

Been there - though on the other side of the equation, filing US taxes from overseas or reporting US earnings for my European tax returns. It's frustrating, to say the least.

Marti - if it's any consolation, you're hardly the first foreigner to get tripped up on what seems to be a simple transaction in US taxes. Next time you'll be aware, and perhaps you can take a loss on something to cushion the large gain. It's how it's done for US investors (and French ones, too, as it turns out).
Cheers,
Bev