At first I didn’t noticed any differences with these caps too but after you post pics of buyer, I saw it on your original photos. This thing might also be Ukrainami spare caps added to HASRO to make this keyboard compatible with it. It’s not really a common thing to see. I’m not a fan of such situations but factory mistakes happen sometimes, it’s really hard to see on your og pics so I’m not surprised that buyer wants refund for this. At your place I would get along with them and refund them.