[tsunagatta]

(For those also missing the context here: the right lean is a consequence of writing straight up/down lines as towards/away from the body when the paper is tilted at an angle conducive to writing right-handed)

Though, I think the author's point still stands here, this could have been done a different way and is largely customary. I am left-handed, for example, and I write up/down lines as parallel to the line of my arm in order to copy the rightward lean, and this also feels perfectly natural -- if right-handed writers had chosen this instead originally, we may have a left-lean on our letters.