Yes, I know about the Babylonian exile, but it is probably the case that the dating on this sort of research has at least a 10% to 20% margin of error. In that case, perhaps the traditional story about the Ashkenazic Jews isn’t entirely right. Perhaps the Ashkenazic Jews are descended from both. In any event, there is nothing obvious that would distinguish genetically the part of the Jewish population carried off by the Babylonians from those that weren’t carried off or that would distinguish those that eventually returned from those that didn’t. I realize that there is folklore on the point, but the Babylonians probably just carried off those that they could seize and who were physically fit.
Alternatively, I suppose that the divergence 2,500 years ago could reflect the fact that Ashkenazic Jews are genetically part Babylonian. In any event, as I said, it is all interesting.
I think it's also almost certainly true that many Israelites of the Northern Kingdom escaped the Assyrian conquest and settled in Judea, so that, by the time of the Babylonian Exile, the "Judeans" already included many of the formerly-Northern Kingdom members of the other tribes.