He means, I think, that method dispatch (i.e. function resolution) in Lisps is less dynamic than in Ruby/JS, where you resolve the call target by searching for the method name in a map -- at least as an abstraction -- belonging to the target object at runtime (or Ruby's method_missing). I am not familiar with all Lisps, but their method polymorphism is usually much more structured.
Actually CLOS (Common Lisp Object System) is more dynamic than Ruby.
Every CLOS method is part of a generic function. Each generic function is a collection of methods. At runtime the applicable methods are collected, based on the runtime class graph of the arguments to dispatch over, and an effective method is assembled by a per generic function method combination.
Method selection is also depending on more than one argument (the target object), but on multiple arguments.
Various parts of that are implemented by a meta-object protocol in CLOS implementations, which make it possible to change the behavior of the object system at runtime in various ways.
