"Very distinct" seems a little exaggerated. Compare the "Autosomal genetic distances" between Ashkenazi jews and other European groups at https://en.wikipedia.org/wiki/Genetic_studies_on_Jews with a similar table of Intra-European distances at https://en.wikipedia.org/wiki/Fixation_index. Finns and French have like twice the distance as Italians and Ashkenazi.

Now look just above that latter table, showing distances between East Asians and Europeans. The distances are far greater--more than 10x.

The precision with which we can identify and track ancestry, often based on small fractions of DNA (Y-chromosome in particular wrt Ashkenazi Jews, not mtDNA as one might think) doesn't imply the degree of genetic distinctiveness.