Silly question

Modules

That description deals with normal mixin functionality, using instance
methods. Here I want to use a module method in another module (or

class)

without qualifying it.

You're looking for Module::included, used like:

module X
  def self.included(mod)
    class << mod
      def foo; "foo"; end
    end
  end
end

class Y
  include X
end

p Y.methods.sort - Class.methods