I think because the original comment is ambiguous. It isn't clear whether by "income I earn overseas", he's referring to income earned while a tax resident of a

I think because the original comment is ambiguous. It isn't clear whether by "income I earn overseas", he's referring to income earned while a tax resident of another country (for example living and working there) or income earned while a tax resident of the US (for example through overseas investment or < 1yr work). One commenter appears to have assumed the former, the person replying assumes the latter.