I almost wonder if she's basing it on him being dark, creepy, and dangerous as she does somewhere state that water spirits are nasty without any hint of nuance.

Of course, the next question is 'why assign him any element at all', but then she divides the humans into strict four-way divisions so why not the spirits? Never mind that elemental bending doesn't work in the spirit world which suggests that the elements may very well be of the material world only...