It can imply isolation, but not necessarily. It is also possible that there are some precursor languages, of which no evidence could be found (yet). Another good example are the Koreanic languages of which modern Korean is a member.
The Ket language of central Siberia has long been believed to be isolate, but was later classified as a member of the Dene–Yeniseian language family (or at least proposed, afaik this research is still ongoing).
The Ket language of central Siberia has long been believed to be isolate, but was later classified as a member of the Dene–Yeniseian language family (or at least proposed, afaik this research is still ongoing).