I'm not assuming my experiences are universal, but there is a more than passing correlation of computer science majors and anime enthusiasts.
So for Emily to have never heard of anime, not just not being familiar with it but completely ignorant of the existence of that word, implies that not a single person ever actually said that word to her or to each other when she was paying attention, even when she was taking college classes in a group of people who generally are more open about 'nerdy' hobbies or interests, and who would almost certainly assume her familiarity with those shows (I've seen similar things happen more than once). She'd never seen any page on the internet, in her life, talking about anime using that word, despite being into computer science enough to major in it.
And yet she, out of nowhere, uses what would be two anime references in the appropriate context during a casual conversation without any prompting. If she'd seen those shows, and mentioned them to anyone else who had seen that show, they somehow never actually used that word when talking about it.
This is like the social equivalent of getting hit with a meteorite on your birthday. Technically possible, but wildly improbable. Her simply messing with Momo doesn't require that bizarrely unlikely series of events to have taken place.