There are Campbells which have mottled coats and I'd imagine that your hamster's pattern comes from the Campbell's side of them rather than the Winter White however if you got him from a pet shop he is unlikely to be a full Campbells as there is likely to be some Winter White in his ancestry too.
Here's a photo of a Normal Mottled Campbell's from the Midland Hamster Club:
Normal Mottled