I'd have to look it up because I don't know the actual truth of it.

That being said, I've heard claims of German ancestry on both sides of my family, so I guess anecdotally that fits with what you've heard. A lot of my living relatives are based in places like Ohio and Pennsylvania which I believe have a lot of Dutch and German influence, so it does make sense.

On the topic of "African-American", that's a complex and nuanced thing that's hardly analogous to white, Caucasian people identifying with their distant relatives such as Irish, Scottish, German, etc so I wouldn't personally consider that being anything even remotely synonymous. It's hard to put into words, other than to say there's no comparison between people whose ancestors willingly came to the USA hoping for a better life versus those who were forced into it with no say on their own part.

Having said that, most multi-generational white folks don't normally call themselves "Irish-American" or "German-American". Those types of terms are usually only used by people, who for instance, their parent literally is a citizen of Ireland or German. Most white people whose families have been in the USA for generations toyingly refer to themselves as Irish, German, Italian, etc because of the privilege and presumption of the "American" part of it, if that makes sense.