The GEN_GenericActions will indeed occasionally play the animation that you specified as sitting animation if the character is sitting at that point. It performs the steps mentioned in the linked "how to make an NPC sit" tutorial internally.
However, the animation name that you specified for the sitting animation is wrong. You have to specify the so-called "simple name"
rather than the animation resource name.
I have just created a page
that provides a list of most available animation names that you can use, and which ones have actually been implemented (only the animations that are actually used in the main campaign have been implemented, and even some of those are still being polished).