Did the groomer say why they shaved him down? If he was matted, then it's faster and kinder to the dog to clip them instead of trying to get mats out. Since a curly coat is not a proper coat for either Cockers or American Cockers, it's possible that he had some mats. At 8 months old, he's probably going through a coat change from puppy coat to adult coat, so the shaving shouldn't have much effect on his coat in the future.
From the KC standard for Cockers:
Coat
Flat, silky in texture, never wiry or wavy, not too profuse and never curly. Well-feathered forelegs, body and hindlegs above hocks.
From the KC standard for American Cockers:
Coat
On head, short and fine; on body, medium length, with enough under coating to give protection. Ears, chest, abdomen and legs well feathered, but not so excessive as to hide body lines or impede movement and function as a sporting dog. Texture most important. Coat silky, flat or slightly wavy. Excessive coat, curly, woolly or cotton texture undesirable.
As an FYI for others, what we in the US call the Cocker Spaniel is usually called the American Cocker in most parts of the world, and what we in the US call the English Cocker Spaniel is usually called just the Cocker Spaniel elsewhere.