Good questions! Unfortunately EEs are not really a standardized breed, so there are not strict rules about breeding them. The 'ideal' EE, in my opinion, would have muffs, willow legs, a pea comb, and lay blue/green eggs. But unfortunately, they can have only one or two of those features, and still be legitimately called EE. To further complicate things, 70% of people/hatcheries that are selling "Ameraucanas", are actually just selling EEs. Ameraucanas are a very specific and well regulated breed that somewhat resemble EEs, but are easily discerned by the trained eye.
Sorry about rambling, the short answer is that yes an EE can lay a cream or brown egg. So that doesn't rule it out.
I think what you might be running into is that the Leghorn father may not be pure Leghorn (I would suspect EE/Leghorn mix). I really can't think of any other way that your bird would get that grey hood he's sporting unless the seller's flock has a stealth roo in it. The white legs definitely finger Orpington as the mother. As Illia stated, it's a dominant gene.
As far as the little guy's size, I wouldn't worry about that quite yet, as some boys take more time on their feathers first, then shoot up like a weed. He'll be respectable in size since he's most likely part Orp.
