Also din't the US soldiers also fought alongside southern Vietnamese and Korean soldiers during the war?

Obviously, the veteran shouldn't have put the weight of his trauma on the young man, and that's not right.

Also obviously, many people who went to war were legitimately traumatized after coming from cultures that taught them to obtain from killing and seriously hurting other human beings, and then being drafted into a situation where they need to kill/hurt other people. Especially when the other people (often hidden among civilians) needed to kill/hurt them.

If his first/strongest experiences with South East Asian people was in a fierce asymmetrical war, it's possible that being surprised would actually put him into fight or flight. I'd like to say he should get over it, but if it were that easy, then such a large number of veterans wouldn't struggle with PTSD.
He definitely shouldn't put it on the young man, but maybe the old guy was just being an idiot.

I guess the comic was trying to imply that the veteran was just being racist, but the picture of the guy's family implies otherwise.
Maybe the author is one of those guys that thinks when a white man marries one of "his women" it's actually a racist act.

If people are going to get past xenophobic instincts, and fully accept each other as "un-hyphenated" members of one society, it at least needs to be okay for them to marry each other.
It's a good deal harder to hate a group of people when one of them is your really nice brother/sister-in-law