Perhaps as a result of reading Harry Potter and the Natural 20, I have problems with the various cameos in HPMOR, including this one. People who have distinctive names and characteristics are automatically marked somewhere in my mind as "important NPCs", but then there are so many of them, and so few of them actually turn out to be important, that the relevant part of my mind gets confused. It's like the literary device where you introduce a character with a lengthy background and description, only to promptly kill them off - except unless your name is George R. R. Martin, you're unlikely to do this more than once per book, whereas Eliezer's version is less extreme but can happen multiple times per chapter.