Not necessarily, although making a crude raft out of logs isn't probably beyond hominids capable of making spear points and hunting in coordinated groups.
But even without boats, consider that the "Flores Men" were supposed to have come to the island about 85,000 years ago. At that time, the northern hemisphere (and presumably the southernmost regions of the southern hemisphere) were in the midst of an Ice Age. This means the ocean levels were lower than today, and it may be that the Indonesian archipelago was actually in many places a contiguous land mass, or at least consisting of islands much closer together (perhaps separated by swamps or mangrove forests rather than ocean.)
An area the size of present day India, around Indonesia went under water at the end of the Ice Age...It is named Sundaland.
An excellent book on the subject is: Eden In The East: Drowned Continent Of Southeast Asia, by Dr Steven Oppenheimer