I would be very wary of this. When people can't find what they need to make their tree "work" for them, they sometimes resort to "borrowing" ancestors and then supplying whatever explanation fits their purpose.
If it isn't documented in some fashion, I would ignore it as unsubstantiated "lore." Put the info in a research notes section of the biography. It might be worth exploring if there is some indication that it could be correct beyond someone "saying" it.