Pre-Clovis ping.
That leads them to such conclusions as the one about Canada's climate being too harsh for the earliest colonists from the Old World.
Actually, those folks were already adapted to life in the high latitudes ~ not at all like modern humans who are more generally adapted to life in the mid-latitudes, or the Equator.
People who could handle 50 below zero weather in Siberia could certainly deal with the same weather in Canada, or other North American habitats. Provided there were sufficient animals around, they could live quite well!
Once they moved South, offspring who were less cold adapted would have a chance at survival and would eventually become more common ~ maybe even outnumbering those who were cold adapted.
At the same time I suppose non-cold adapted people with boats could probably make it from Sundaland to California in just a few years ~ more or less ~ but I really wonder about that leg from Northern Japan to Vancouver.