That is correct, yet based on evolutionary chains, our ansestors would have been spread among the world on all of the pieces of pangea, which unless africa was the only place for these lifeforms to survive we would have evolved all over. Im not saying I believe this, its just a theory. Heck we could have come from aliens for all I know, I wont really know until i die, and still maybe then I wont find out the truth. But as for chinese making it to the americas, I dont doubt it. Anything is possible. Like Mr. Muhamad Ali sayed "Impossible is nothing" its all fun to speculate historical situations like this but the fact remains that we dont really know for a fact. Because if we did there would not be any conflicts of opinions.