The following is a paragraph from a brief history of Clan Dhuibh. Can someone explain it in a way that I can digest it?

"[Wemyss] became the surname of a cadet branch of the Royal House of Duff, descendants of Gillemichael, who was the Earl of Fife early in the 12th century. When senior male lines of MacDuff failed, that of Wemyss became the Chief of Scotland's senior clan, although it never reverted to the patronymic of MacDuff."

Does it mean that the MacDuffs were unable to produce a male heir, so the Wemyss family took over and changed the name?