Could have been from some of the plant life. There certainly seemed to be an abundance of native flora and fauna that took sufficiently different forms from the standard leafy greens that it isn't implausible that the "feathers" were really plant-based.

Then again, it's a made up world in a sci-fi movie; there is a long list of things that wouldn't be "implausible."

Didn't those hammerhead things have feathers on their heads?