It's a bad title in the press article. The title of the research article is "The New Genealogical Tree of the Da Vinci Family for Leonardo’s DNA. Ancestors and descendants in direct male line down to the present XXI generation". The total number of relatives usually grow exponentially, but the number of relatives in the direct male line usually does not grow.
edit: 14 is actually quite a low number for the 15th century, especially if he had 22 half siblings...