Yes, I've also heard that feather picking is caused by protein deficiency. But if it's not curtailed, it will quickly develop into a bad habit, and good luck trying to break a chicken habit. Our feathered friends are really stubborn about changing their ways!
Very recently I noticed my little EE pullet Flo plucking feathers out of the face and neck of her former brooder mate. Flo is a bit under-sized and since she's either at the bottom of the pecking order or close to it, she may not be getting access to as much food as she needs. I immediately started giving Flo an ounce of canned tuna every other day, privately away from the rest of the flock. She's been getting this therapeutic treat for two weeks now, and I've not seen a single incident of feather picking since.
Whether this is evidence of a protein deficiency being satisfied or something else, I can't say for sure. But it's certainly a simple remedy to give it a try to see if it'll help your feather picker.