This reminds me of Feynman saying "Yeah, I took the door" and people later thinking he'd lied and denied it: http://home.agh.edu.pl/~szymon/humor/feynman.html

We usually don't memorize things we see or hear (or say) word for word. We translate them into the meanings and reconstruct them from that. And if we don't correctly understand the meaning, it makes sense that we don't remember it accurately.