Yes, I was thinking the same basic idea, but not necessarilly the celts..
I think another group came from Sundaland..
Those "olive skinned, almond eyed" ones..
I believe the Jomon/Ainu group (Kennewick Man/Spirit Cave Man) dominated most of Asia in prehistoric times and today's modern Asians and Caucasians split from this group. The oldest undisputed Mongoloid skeleton ever found is only 10k years old. (Professor Stephen Oppenheimer) The oldest Jomon skeleton ever found is 13k years old and was found in Japan
Marvin Harris (bless his soul) got me interested in anthropology. I read his book, Our Kind, and was hooked.