The story is from Centralia, Washington. Perhaps the parents lived near the border and had gone to Vancouver or some other place just across the border—the traveling may not have been a very long distance. If the 95-year-old man has relatives in Canada, perhaps his parents were visiting relatives there then.
I wish there were more info in the story, like why they were in Canada. Did they live there? Perhaps a visit, yes. And why did he himself question his citizenship in the forties? My sister was born in Germany because my Dad was in the military. She’s never questioned her citizenship. I just wonder if there’s something left out of this story. Maybe not, but it just seems thin on info.