This is a nice article about how that conclusion is reached.

https://dna-explained.com/2016/09/14...tive-american/

"We do know that haplogroup X2a is indeed Native, as is X2g and possibly X2e. So some of haplogroup X2 went east, incurring mutations that would become Native American haplogroup X2a, X2g and possibly X2e while others went west, winding up in Europe and incurring mutations that would become haplogroup X2b and subclades."