How did he know there are two types of pad fitted?? They don't have time to strip the pads out to check?? Most Mot testers wouldn't fail pads unless the braking was compromised or the reed was dragging!! There must be more than 1.5mm of friction material for a pass according to the guidance!! But they do add that it's at the testers discretion
If you find the pads are serviceable you can appeal but it's not woth it for £20!!