I haven't seen Avatar but from what you've said it sounds like fanon. It's either an idea a lot of authors liked and so latched onto, or the product of people who don't know the show very well so felt the need to fill in the blanks rather than research.

I dislike most fanon cliches because they get used to death (Ex. Zelenka's still) but despise them when they make absolutely no sense (Ex. John escaping the infirmary for no reason when he's still severely injured). In my current fandom there was talk about one character being claustrophobic even though A: it was never mentioned in canon except as a means of distraction and B: considering what the character does it makes no sense that he would be claustrophobic. However, this particular piece of fanon is getting nipped in the bud pretty quick.