The word domestic in GDP is the key to your answer. That means only income that was made in the United States (domestically) can be counted in the GDP.
The sentence you want to pay attention to is
GDP does not include income received by (sic) other countries. This sentence should read
GDP does not include income originating in other countries. No matter how it is written, that is the sentence you want which tells you what not to count.
You can only count income that originated in the United States.
The sentence you want is the last one of the first paragraph.
