The light-haired one on the left is holding the quill properly and has not splattered any ink, unlike the other two. This guy seems the type to regard languages he doesn't understand as being inferior babble/scrawl, or not even language at all. Taken together, it seems likely the one girl is already literate, (Edit: the follow up confirms this) and that in general he is seriously underestimating them. Also, I just noticed that all three have horns. I had assumed they were elf lolis; not sure if there are supposed to be some implications there. Maybe they are older than he thinks?