Use User#uses_external_authentication? for checking that

app/models/user.rb

@@ -356,7 +356,7 @@ class User < Principal
 
   # Does the backend storage allow this user to change their password?
   def change_password_allowed?
-    return false unless identity_url.blank?
+    return false if uses_external_authentication?
     return true if auth_source_id.blank?
     return auth_source.allow_password_changes?
   end

app/views/users/_form.html.erb

@@ -54,7 +54,7 @@ See doc/COPYRIGHT.rdoc for more details.
 
 <div class="box tabular">
   <h3><%=l(:label_authentication)%></h3>
-  <% if @user.identity_url.present? %>
+  <% if @user.uses_external_authentication? %>
     <%= I18n.t('user.authentication_settings_disabled_due_to_external_authentication') %>
   <% else %>
     <% unless @auth_sources.empty? %>