The problems with these types of tutorials is that they always go out of date, this one is 5 years old so some things have changed. For the add menu, see release/scripts/startup/nodeitems_builtins.py.
In general it’s good to pick another node name that is not used much elsewhere in Blender, and then search for it in the code and check that you have modified all the same places. For example “despeckle” could be good in this case.
Another problem is that the information in the wiki is scattered all over the place, and by the looks of it duplicated as well, last time i needed to add a compositor node, i used https://wiki.blender.org/index.php/User:Sobotka/Minimal_Node_Code as a guide. never found the page you found