I'm still kinda on the fence as the breeder I got "it" from states that some of her hens have large combs...at times I think def a roo and at other times a hen? But the other day when "it" was out in the run a standard size chickens decided to check them out (through the fence) and "it" was puffing up and charging at a standard size hen? I would say that is rooster behavior, No?
Our little guy did that puffing up at the fence thing too while our pullet was totally uninterested in our big girls. However... back a few pages on this thread someone posted (I cannot remember who) that she had what she thought was a pullet until it started mounting the other chickens and crowing. Several members said that a pullet with dominant behavior in a flock where there is no rooster is capable of crowing and mounting the other chickens.
Please post some more pics of your little "it".