The Census Office only carries out the directives of the Congress.
In fact the 1902 Act clearly states exactly what information the Office could collect for that particular census.
Congress never gave up their authority.
The actual Enumeration shall be made within three Years after the first Meeting of the Congress of the United States, and within every subsequent Term of ten Years, in such Manner as they shall by Law direct.
Title 13 of US Code: Census <- there's the "by law direct" stuff