The “not to be considered a naturalized citizen” has been in the FAM since at least 2007. Here is the archived version:
https://web.archive.org/web/20070817162959/http://www.state.gov/documents/organization/86757.pdf
Previously the “not naturalized” section was 7 FAM 1131.6-3 Not Citizens by “Naturalization” but when they removed the part about eligibility to be President, they renumbered it.
Ah ha. Thank you.