Could be.
But at 97 my father had the same problem but even so he could do all of the basics. He knew right from wrong, good investments from not good, proper behavior, etc.
Of course if the guy never knew the law, he could not retain it in short or long term memory so I will stick to my theory that it was the case of a guy with a gun with little or no knowledge of the law.
You see it every day on FR and shooting message boards: “If someone ___(fill in the blanks) and I catch him.....blah blah blah”
Wanna be Rambos who will eventually end up in deep doo doo.
Well... as they say, ignorance of the law is no excuse.