It's not an argument. It's a fact. Mr. Root was in the class of '83 in Poli SCi just like Obama but doesn't remember him. Nor, he claims, does anyone else, including the legendary professor Henry Graff, who also does not remember him. Not an argument. A fact.
Caution: anecdote ahead. Once, I went to a bar and the person working the door said (approximately), "Hey, [BenjaminTR], I was in your class last year." I did not remember him. After a while I was able to convince myself I vaguely remembered him barely. Just one year later I did not even recognize the guy, and I only taught one class per semester the year in question. Not everyone stays in your memory for all time. Sad but true. (Though obviously the lack of recognition event stuck with me.)