Sounds like you're thinking this might be crossed with a Cornish broiler. They do not breed true. So if you were able to bring 2 Broilers to breeding age and successfully bred them the offspring would just be like normal White Rock/Leghorn cross.
Both Orpingtons and Barred Rocks have the potential to be very large. I had a Barred rock rooster that was 22lbs and was larger than my Jersey Giant Roo. Chickens like people are individuals and very in size and temperament. This is especially true when you cross unrelated breeds. "Hybrid Vigor" is the term.
I your case from what i see, there is no reason to question the hatchery description.