Now that's surprising, but not impossible. It is possible the X haplotype simply died out in Eastern Asia -- it's nowhere particularly common -- or perhaps one woman, or a small population of closely related women, could have traveled from the Near East to America or been brought as captives during the migration. But it is fuel for an alternative and not completely impossible hypothesis that there was a second, parallel migration route into north eastern North America from Europe.
Fascinatingly, Kennewick Man's sequence is perfect basal X2a. What that means is no one with that basal haplotype is living today, but we can infer(and in fact already had inferred) its sequence from the sequences of all its descendants, which have all diverged some distance from it. So it's likely Kennewick Man was reasonably closely related to the ancestress of all current American Indian X2a individuals. A mitochondrial sub-Eve, if you like.
Yet even more fascinating is that, because of this divergence, Kennewick Man's mt-DNA differs by at least 5 - 15 base pairs from all living Native Americans. But it's only 4 base pairs distant from X2a'j, the common ancestress of X2a and X2j. And X2j is found, not in America, but in Tuareg tribesmen in the Western oases of Egypt, and a single Iranian. This could, of course, simply be a recurrence of the same mutation. Further up the mitochondial tree by one branch and one base pair, it connects to a single Druze living in Syria.
What migrations led to this result is a mystery still shrouded in the mists of time, but as of now, the Solutrian hypothesis is still alive, though barely.