I would assume he had one because he used it to type the damn memo.
Here's one of Bush's other documents. See page two, second line down, dated 4sep60. A single-symbol superscript "th" in fixed-width font. So both proportional fonts and single-symbol "th"s were in common use at the time, and you find it suspicious that a Lieutenant Colonel might have a proportional typewriter (30 yr old tech) with a "th" symbol (available even on fixed-width fonts) on his desk.