Any club can be a commercial venture, and most flying clubs are just that, but there's nothing wrong with this, and no need for the airfield to be licensed for various business activities to take place there. Instruction for the PPL cannot take place from an unlicensed field, but a suitably qualified instructor or commercial pilot could conduct other training or commercial activities, subject to the terms of his or her licence. A PPL cannot earn money from working as a pilot, but can own a flying business.
On this basis, the suggestion made in the published letter that there might be some regulatory problem with the airfield's activities is not easy to follow, as there's no reason to assume that the pilots concerned are not appropriately licensed for what they're doing.