Most companies don't collect nationality information, so there is no question in my mind that the program (if it collects more than metadata) has spied on Americans, in violation of the law.
If I sign up to Yahoo France, while in France, and give my French address, I assume the NSA (or Dutch AVID, in this case) would assume I'm French and could spy on me. But this may be incorrect, I could be an American... Yahoo never asked me nor verified my identity, let alone my nationality...
Even if they did, some people are dual nationals, and some people are nationals of the US and the US doesn't know about it (Children of Americans born and raised abroad, who have a foreign nationality as well, have no US birth certificate, never lived in the US, have no SSN, and have not yet asked for a passport). These unregistered people are Americans, too, the law says they cannot be spied on without a warrant...
The NSA would have to be able to prove that accounts do not belong to Americans (impossible, for many reasons).