I think the sentence refers to the Replacement model, which sez that there was only one population of modern humans, it originated in Africa, and spread out across the Earth, overland, extinctifying all other species of homo (and a great many non-human species besides), beginning about 50,000 years ago, or less.
The alleged bottleneck was 24,000 years or so earlier than that.
The model doesn't hold water regardless.