If the person quoted had seen a wall calendar, he/she would have described it that way. To me it sounds like he manually drew the boxes onto a sheet of paper. A guy this organized would do something like that.
I used to do things like that (the engineer in me) until tools like VisiCalc made it a lot easier to do on the computer.
Perhaps - that doesn’t seem like a huge distinction. Still a months worth of days per page - and small boxes for notes. Maybe he was a tiny writer.
Kavanaugh’s 1982 Wall Calandar here