Could be a valid scenario. But where are the artifacts, or rather evidence. I am not saying that they aren't there. Just that it is good scientific procedure to hypothesize and then search for evidence of your supposition.
What about native american, specifically Lakota Souix legend of Buffalo Woman, who appeared as white, then brown, black and then yellow off in the distance (I may have my order of colors mixed up) and who taught the people how to live in harmony? Then promissed she would come back and usher in an era of goodness for the people.
There is a lot of human history, when put under a microscope and with the concrete knowledge that we have been visited for some time, that may be seen in an entirely different light.
But again, scienitifically, we need to prove or disprove our hypotheses.
The Appropriateness of Chance is Astounding
Persephone