It affects more than humans. I am almost sure of it.
Humanoid means human-like, we in two arms and two legs.
It does not specify "normal height" humanoids or all humanoids which would include giants.
Goblins, orcs, alchemist, shaman, skeletons, etc should count here. You'd be surprised, feel free to experiment.
I think it is a fun skill to have and might make for some very fun Impossible No Loss runs.
Opens up more options for different units.