The cynic in me reckons that was a (shortsighted) attempt not to have to eat the loss from a kilo of beans. If you had asked for a refund directly rather than just telling them it arrived open I expect they would have immediately obliged.
It was the wrong thing for the roaster to do because it has the potential to discourage potential customers from privileging that roaster with their business. They could potentially lose more than the wasted kilo which he should have immediately recognised as just the “cost of doing business.”
The “artisan roasting” market is pretty saturated; there are more beardy hipsters wanting to roast coffee for a living than there are customers willing to pay £40 per kg of beans. And their customer base is pretty well connected what with fora like this - bad news travels fast. A good reputation is valuable, and equally the opposite applies. In a saturated market service and reputation is all you’ve got.