My cockerspanial has less fur

English Cockers don't have nearly as much coat as American Cockers. Working or field line dogs will have even less. That said, at not even four months, he's still got his baby coat. When his adult coat starts coming in, chances are it will be longer, but he didn't look like he's going to have as heavy a coat as a show line dog.

If he's not from a reputable breeder and doesn't have papers, yes, there is the chance that he's mixed with something else.

In this picture though, he looks like he is from field or working lines. A distinct "type" split between show and/or working line dogs versus show line dogs happens in a lot of breeds, and field and /or working line dogs and show line dogs can almost look like separate breeds.