"But then... what does the university do? How is magic taught without books?" Is she a sorcerer?
Then the rest of her questions hits him and Ahmose is mortified. He has no idea how he does magic and it's the most embarrassing fact about him. But he really can't see how to avoid this, and he kind of promised them an explanation of his portal spell, because just showing it without explaining anything isn't really fair.
"I... don't know exactly how," he confesses. "I wasn't formally taught. I have just a little bit of magic, other than the portals. I asked the wizards at the temple of Nethys, god of magic, and they said I was probably a sorcerer, but that I couldn't ever become a better one because I wasn't splendid enough." Actually what they said was 'there are as many kinds of mage as there are mages' but he's pretty sure that was just exaggeration. "But they also said a cantrip couldn't make portals, so maybe they got the other part wrong, too. I didn't show them the portal spell, because I was trying to improve it so I could get more when I sold it. And one of the things I tried was to make portals to other planes, and that's how I ended up here."
"When I do magic it feels like - I have a sense for it? Like knowing I have an arm, and where it is, and how to move it somewhere else. I just know I can do some things, and how to do them, with the gestures and the words. So I can cast light, and mending, and the laundry spell." Only true wizards can pronounce the name for the laundry spell without stumbling, everyone else just calls it the laundry spell. "And the portals. They all feel the same to me."
"Wizards learn magic from books. In general, and specific spells. They charge a lot of money for letting other wizards copy their spells into their own spellbook. And every time they want to cast a spell, they need to read it in their book again. Or, well, they read their book in the morning, and then they can cast those spells later, but only a few times and only the ones they read. It's like they can only remember a few spells at a time, and when they cast them they forget again."
"Anyone can learn to be a wizard if they're smart enough, you don't have to be born with it or anything. Sorcerers are said to be born that way, but they only develop powers as adults and most sorcerers don't have sorcerer parents, so I don't know if it's actually true. And of course clerics are given magic by gods, who can choose anyone to be a cleric. I think." He feels extremely unqualified to be explaining magic, but he has actually practiced this with some of his neighbors who asked him about his time in the big city, so he delivers this without stopping or cringing.