Why do people claim they crossed over to Canada from the US border by mistake?

A recent Reddit post on a person claiming that a friend, a Palestinian refugee, went inside Canada from the US border and then got detained while coming back has triggered a major debate on such claims. This particular incident goes like this: the Redditor said a friend and the friend's boyfriend wanted to see the US-Canada border in Detroit.

Raccontata datimesofindia.indiatimes.com