When my mouth wasn't moving properly, I also had problems with homophones in writing. The sounds and meaning somehow got disconnected. Heal-heel, their-there-their-they're, all of a sudden the wrong one would come out when I was typing. And I haven't ever done that before. Not even at my most demented moments.
Although this wasn't a sign of misunderstanding the point of the sentence, it does indicate another lack of executive function and does make one unfit to be President. Words Matter.