It is Ancestry.com conducting the masquerade, not the passenger list! There are other purported "reconstructed" or "early census" items that include stuff like names from a letter, a militia list, or obscure tax assessment lists.

A "reconstructed" census using other data has a little bit of logic, when a census enumeration did exist but has been significantly lost. However, it is much more sensible to present the original data for what it was -- and immensely more useful if all of the original data is included together with a proper citation.