Definitely a cockerel.
Orps are slow to mature, my English Orps didn't start crowing until 4-5 months. We first thought we had 1 cockerel and a bunch of pullets, but the subordinate cockerels were just hiding behind pale pink faces until they were almost full grown. So when I see those red faces like your boy, it's a certainty. Surprising that the breeder couldn't tell.
I don't think he's mottled though. The pullet is split to mottled (a carrier, most of her spots will disappear but her chicks could inherit it). The cockerel has only the slightest bit of white on the tips of his feathers which doesn't really look like the mottled gene. Pictures of him younger would help to be sure though. My avatar pic is one of my split to mottled half Orp chicks.
