The Orpington hen isn't really that small. Plus one thing I noticed about show quality Orpingtons, they're really more feathers, and fluff rather then actual size. Their extra plumage makes them look bigger then what they really are.I think the show thing came in to compare your rooster to a SOP bred silkie.
It was to show yours is a hatchery quality bird which would explain his size.
Your Orpington hen is also hatchery quality which explains why she is small.
I'll place my big roo next to my jersey giant hen for comparison for you, how does that sound?