Stand up and try to hold your arms out in front of you, with the palms facing straight down.

You'll find that this is a little awkward. The natural resting position of your hands is with the palms facing inwards, not down.

Yes, I cant see in the article that actually define the term!

https://www.alamy.com/portrait-of-funny-lovely-european-girl...

> Portrait of funny, lovely European girl with rabbit ears, imitating bunny, holding hands like paws and looking up daydreaming

They are referring to the pose people take when they are pretending to pose "like a bunny".