No, I don't think so. Behind the slightly odd syntax CLOS is a very traditional OOP system. In my example in the article there's even type checking in the method:

(defmethod some-user-greeting ((user some-userc) &optional daytime) ....)

means that the argument 'user' to the method MUST be an object of class 'some-userc'.

EmacsLisp's CLOS doesn't have as much type checking as CL's but it is there.