Checked on this (help links are a choice made by each app author), and it is believed that this was intentional because the Button Rule 5.x (the grandchild app where you actually edit the actions) is effectively the same as the Rule 5.x editor. I've added a note to the Rule 5.1 docs to indicate this, though I can understand why this might be confusing.
It should also be noted that if you are in the "child" Button Controller app, the docs will go to those for Button Controller (also linked to in the post above) that do describe that particular interface. So, what docs you end up at depend on where you are in the parent/child/grandchild apps that make up Button Controllers.
