It's preference, obviously. Which is what the question had been seeking, and Robby doesn't look at Midoriya with judgment, really. Just the curiosity, which lingers on even as he's shown the notebook and everything the other guy has been saying. Robby doesn't exactly try and read too closely at anything, but simply takes it in, in its entirety.

"You take notes like this for everything?" There is a note that's impressed there. Robby doesn't; he goes over everything in his head, asks Mister LaRusso or Tory later one about anything he's not sure of. He read books; he had nothing, so he practised, over and over and over.

This method certainly has its value.