Why is my chicken so small?

[Kitkatkate]

I have had this Wyandotte hen for three years now and she is 5lb. She was normal in size and growth as a chick and has always been 5lb. as an adult. I didn't realize she was supposed to be bigger until this weekend when I saw my friend's Wyandotte and noticed she was significantly bigger. Is she a dwarf or something?

 

[CascadiaRiver]

A lot of feedstore birds tend to be much smaller than the "Standard" Sizes, I would say shes a bantam but Bantam Wyandottes are about 2lbs XD