After all, they must have got the information on ancestry from somewhere.
It's best to be very wary of 'research' that others have done on ancestry.com, unless scans of documents etc are attached as files. Especially if it's family trees done by people across the Atlantic, in Australia etc. They've often just accepted pop up suggestions from the website and made connections between individuals in the past that are unrealistic but which look interesting/convenient. I've had that issue myself.
It's better not to accept the suggestions that come up, and better not to take other online family trees as gospel.