The only relevant citation you've provided said that he testified as a private citizen, not that he testified as a US citizen. Take in context, it seems clear to me that the phrase is there to distinguish between him testifying as an individual as opposed to testifying in his official capacity as a head of state.
Do you have any evidence to support the contention that Netanyahu has claimed to be a citizen of the US?
Well, dueling has been illegal in the US for better than two centuries, so that shouldn't be surprising. If you mean "dual citizenship," I'd bet there are a bunch of American Indians who will be surprised to find out that you've been granted the authority to revoke their dual citizenship status.
Also see http://travel.state.gov/content/tra...ip-and-dual-nationality/dual-nationality.html
Lol...