I confess that I am puzzled as to how the US government even knows about a person born of US parents in another country that has lived there into adulthood. There is no SSN so they should not exist, as far as the US gov is concerned. At least, that is how I would have assumed it worked if it happened to me.
I don’t know, either - however, I think it shows the tenacity of the IRS in tracking down anyone they think might be “shirking their responsibility”. The US Government is putting a tremendous amount of resources in identifying citizens and legal residents living abroad all in the name of tax enforcement.
If only they put that same effort into controlling illegal immigration...