ruby responding to one method but not to other in the same scope

With the following code

class User < ActiveRecord::Base

  # ...
  # code filtered from here
  # ...

  # both methods below are public methods

  def humanized_roles
    roles.collect {|e| e.name.humanize }.join(', ')
  end

  def role=( arg = nil)
    self.roles = []
    self.add_role arg.to_sym
  end
end

This is happening

[2] pry(main)> User.new.respond_to? :humanized_roles
=> false
[3] pry(main)> User.new.respond_to? "role=".to_sym
=> true

rvm, ruby, rails versions

rvm 1.26.3 (latest) by Wayne E. Seguin <wayneeseguin@gmail.com>, Michal Papis <mpapis@gmail.com> [https://rvm.io/]
ruby 1.9.3p448 (2013-06-27 revision 41675) [x86_64-linux]
Rails 3.2.14

Am I missing something obvious?