A reasonable guess.It might make sense to add a note to the Elisp manual, in node `Character Type' or node `Character Codes' (where we talk about `characterp'), or both, to point out that Emacs Lisp characters are not the same as Common Lisp chars.

 

I assumed that `characterp' and the `character' type class was connected in Common Lisp. If they aren't I guess the current system makes sense.