I very much doubt anyone could know this. It’s probably part of the sick master-race crap that the British are peddling, known as The Replacement Theory.
I heard a fascinating theory - that Europeans and people in general were much taller and slimer pre agricultural revolution - more like African Masai - and that the switch to grain based diet stunted our ancestors.
Only now with meat easily available as part of the diet have we reached the height level of the hunter gathering ancestors.
I had always assumed our ancestors were tiny to start with. If you visit Europe and pass by homes occupied since the late middle ages you can see by the door frame size how small people were until just recently.