He is probably alluding to the Khazar hypothesis, according to which at least part of the Eastern European (and thus Ashkenazi in general) Jews have Khazar asc

He is probably alluding to the Khazar hypothesis, according to which at least part of the Eastern European (and thus Ashkenazi in general) Jews have Khazar ascendancy. The scale is very much subject to discussion, but genetic evidences[0] support the core idea. [0] https://academic.oup.com/gbe/article/5/1/75/730630 https://academic.oup.com/gbe/article/5/1/75/730630