You’re reaching a bit here. He went by “Barry Obama” from the time he moved back to Hawaii circa 1970. There’s no reason the NZ guy would have remembered him as much more than “Barry the black guy down the hall.” I’m younger than Barry and I can barely remember any of the last names of white students beyond my close group of friends at college, much less the “strange ethnic” last names of people in my dorm one year who were Indian etc etc. Barry went to college (only 2 yrs @ Oxy remember) under the name Obama and any foreign student aid he got was due to his Kenyan origins, not his Indonesian connection.
I agree with you, it is a stretch. As for remembering people from the past, I can not remember maybe ten that I graduated with and that might be a stretch.