Imho, everything comes from the macro, and the fact that you mash it.
Here's how I interpret the sequence:
1) You are in human form, and you mash the macro.
2) You turn into a cat, and a 1.5-sec GCD occurs.
3) If you queue another "cat form" shapeshift (on accident), the game would proceed to remove your current stance.
4) However due to the GCD, the game doesn't allow you to enter cat form again.
It doesn't seem to me that Kripparian's video applies here.
Kripparian explains it here:
https://www.youtube.com/watch?v=VgDjG_0ecTI&t=188s