Have no clue what the German guy said in German, but I've got a different question...
Greentradertax says the German owes US tax on the income reported on his K-1. Well, what if he doesn't pay it?
a) Germany extradites him, or
b) Germany doesn't care, but the IRS will report his name to border control and the guy better not come to the US, or
c) Germany doesn't care and the IRS cares but doesn't do anything. He can come and go from the US as he pleases, or
d) the IRS makes a claim on the person's assets in the US, or
e) nothing.
My guess is e. d would make sense, but I think the IRS needs a judgment to garnish assets and I think they only go through that bother for really big fish.