It might have been sort-of true then, if they didn't know how to make good chicken food. Chickens that forage for their own food will find a lot less in the winter than the summer, which could result in several months of underfeeding for the ones that were trying to grow up in winter.
I know that underfeeding can stunt a chicken's growth.
People do it deliberately if they have Cornish Cross meat chickens that they want to breed from, or keep as pets. The stunted growth lets those birds live longer than if they are fed free choice and get really large.
We also see pictures of stunted chickens on here sometimes, from people that get chickens but do not know what a chicken needs to eat. They come here to ask "why aren't my chickens growing?" After they buy proper chicken food, the chickens grow better, but some never do catch up in size.
For the original poster's chicken, I think she will probably be fine, without any long-term health effects. She probably just has the genes to be slightly smaller than some of the other chickens. Some chickens can be over 10 pounds at maturity, but some others only weigh about 4 pounds at maturity and are not considered dwarfs (example: Hamburgs.) Bantams can weigh under 2 pounds, and all those sizes can be perfectly healthy and live long lives.