I've seen that so many times. People are told to add cat food for protein. I look at cat food labels at the pet store so it can be anywhere from 11 to 30% or more. So just saying cat food isn't the answer. It is feeding something that is actually higher in protein than chicken feed. Some canned cat foods don't fit the bill, some dog foods don't and definitely eggs aren't higher than chicken feed.
Good point and one that is easy to overlook when you are accustomed to only purchasing and feeding high quality pet feeds such as cat foods that have high animal protein content - it's easy to forget that not all pet foods are so well made.