Along with other new evolution methods such as:
- Pancham -> Pangoro
- Eevee -> Sylveon
- Sligoo -> Goodra
They were all revealed by Gamefreak prior to the release of the games.
I couldn't really find a site where it specifically said they confirmed it but I found someone saying something that pretty much confirms it.
>Do we actually know you need to hold it upside down, or is Game Freak just laughing at us?
Source of the quote above.
Hope I helped.