Board Thread:General Discussion/@comment-35086897-20180410025240/@comment-30530552-20180417160440

One could say the same thing for the bird transformation thing both Qrow and Raven could do. Until Raven proved magic exists and Ozpin called it out next episode, they hadn't explicitly said it was magic, YET ever since Qrow mentioned "hey, I got a Bad Luck Semblance, not a birb transformation power" in Chapter 8 of Volume 4, we could logically deduce it was magic even if it wasn't explicitly confirmed.

It's a similar situation here. It's not an aspect of Ruby's Semblance (or anything remotely close to it), if it were Aural based then we would likely see other examples, and it'd be called out specifically as that, and not a rare trait. Not to mention, 2/3 of our examples of magic (Maidens, and Ozpin; no confirmation yet on Branwen Birb powers) are passed on, it's not hard to assume that a genetically passed-on power (thought to be a myth) exists. The rarity also seems to suggest it as magic.