The German ancestry is Americans in exaggerated. People in the USA tend to overstate their non-British and "American" (colonial British) blood because they think is more exotical.
The majority of the ancestry in the USA is still mostly British (Irish, English and Scottish) because the British had a founding effect in Americans. But yes, German is also a major component and quite large. Most Americans are probably a British + German combo with other minor ancestries (something like 45% British, 35% German and the remaining Scandinavian, Dutch, French, Italian, Polish, etc.). Off-topic though.