If populations A and B share a haplogroup it does not imply that population A is B's ancestor, or population B is A's ancestor. No present-day population is the descendant of any present-day population, though both populations may share common ancestors. The common haplogroup is probably inherited from common ancestors.
When you say "Egyptians" or "Vietnamese", in genomic studies you generally mean present-day people. People living in present-day Egypt or Vietnam may be related to each other, but they cannot as groups be each others' descendants. It is more likely that there is some ancestral population that is the common ancestor of both groups that carried the genetic variant. The only exception I can imagine is a VERY recent colonization (assuming there were no indigenous people in the colonized country, which is effectively never the case).
To take this specific example, it would be most likely that at some point in ancient human history the expanding human population (from e.g. out of Africa) had people carrying a haplogroup that settled Egypt, Anatolia, and Vietnam in independent events.
Therefore none of those groups would be descended from one another. Each population was founded by the people who stayed in that region, not the related people who left and colonized other regions.
Sampling of ancient DNA makes the question more interesting, if you for example found 20,000 year old bones sharing the haplogroup. Maybe that is a descendant of one or both populations. But again the relationship of that ancient individual to present-day geopolitical borders would still be fairly meaningless without a lot of supporting data.
It is additionally possible that the haplogroup arose independently in two different populations. This is sometimes called parallel evolution or convergent evolution. In this case there is actually no relationship at all between the populations. While this is much less likely than common descent, it is nonetheless a hypothesis that you need to reject before you claim that one group are the descendants of another group.
I hope that this helps!