I'm not sold on the hypothesis that Europe and Asia were way ahead technologically, because honestly (mostly Europeans) did all they could to eliminate any culture indigenous cultures in the Americans and Africa, ignored them and devalued them completely. And definitely didn't make any attempts to understand or document what was going on before they got there. So likely lots of informaiton got lost along the way.

Yes, proximity helps with cross pollination - but there are hundreds of distinct ethnic groups in the Americans and Africa that also traveling, cross-pollinated and shared. History decided to group them together and call these all one big group.