Sure, its contributors are from all over, but
* It was started by a German living in Germany while a student at a German university
* Its current-day non-profit backing org[1] - which owns the KDE trademark and represents it in legal matters - is headquartered in Berlin.
[1]: https://ev.kde.org
Even at the time, he wasn't a sole contributor. He posted to a Usenet board and gathered interest of a multinational group before commencing. Today, it's even harder to make that argument considering the minority of KWin, Plasma, etc commits come from Germans (or even Western Europeans).
> * Its current-day non-profit backing org[1] - which owns the KDE trademark and represents it in legal matters - is headquartered in Berlin.
Sure, KDE EV is German. And both the Linux Foundation and FSF are headquartered in the US...yet you would probably take umbrage with GNU/Linux being called "American" for that reason. You have to incorporate somewhere and it's probably going to be somewhere in North America or the EU.