Doesn't look like an Orpington at all, sorry. Where are you located? They may have Cuckoo Orps over in the UK, but that body type doesn't seem Orp-like to me.
Either a Barred Rock or Cuckoo Marans--can't tell about the leg color. Should be yellow for a BR.
I'm not sure it's a cockerel, personally, but it's no Orpington. How old is that chick? Legs look pinkish so could be a Cuckoo Marans or a cross of BR x Marans.
I once did get a rare weird throwback from my blue Orp x RIR/buff Orp hen who had barring, a hidden gene coming from when Sandhill Preservation used Plymouth Rocks to offset inbreeding in their blue/black/splash Orps, but his barring wasn't clear like that one. That isn't an Orpington.
I know it's not a cuckoo marans, because the egg was more the color of an orpington egg.
It was born on May 27th, so it would be getting close to 8 weeks old.
Hatchery Cuckoo Marans don't always lay dark eggs. I've had a BR hen lay an egg every bit as dark as some hatchery Marans stock. But, if it was a very light tan color, then you most likely have a Barred Rock chick there. The leg color is not right, but some bad stock has off-color legs. It should be much more yellow for a good Rock leg color.
I'd ask the seller if she/he has Cuckoo Orps. Could be she mixed up the eggs. It happens. Maybe a simple mistake. Are they all like that chick? The thing is that the feathering doesn't seem Orp-like to me.