Was thinking some kind of deformity too.That doesn't look like any CX I've ever seen. Not only is it small for a 3 month old CX, it looks to be fully feathered. CX don't put as much protein into growing feathers so they tend to look kind of ragged.
I'm wondering if maybe it's a Leghorn with a leg injury/deformity.
It is an odd looking bird.....it's wing looks a bit wonky as well as the lack of breast muscle.