There is no way for him to prove he didn't copy and paste it, but there is no way to prove he did either.
I tend to think he did have it memorized, since it's off at the 21st and the rest of the consecutive digits and copying the wrong number is just silly. I'd imagine that tends to happen when you try and memorize 28 digits.
Interesting, but I tend to find pushing the pi button a lot easier.