Question:  How likely do you think that wooden objects, made by people, floated across the oceans and ended up on far away beaches in prehistoric times?
Personally, I think this was more common than people making these journeys.  It's kind of a no-brainer.  Can you imagine discovering a dugout canoe from Europe, for example, filled with various objects like stone blades, bows, arrows, pottery, etc. washed up on a North American beach?  Or perhaps the other way around?  Humans have been making, and losing, stuff for tens of thousands of years.  I don't see why there is such debate surrounding how technology was spread in prehistoric times.