You are supposed to be taking the Oath in Canada. Since most of the ceremonies are now virtual, it's hard to see how they can enforce that rule. Nonetheless, there are extremely rare cases where someone can take the Oath overseas but that is in unconventional situations like discretionary grants. Your friend most likely declared that he is in Canada during the Oath ceremony when he was not.One of my friend told me they took the oath ceremony in Japan. Is that possible?!