1. Dealers will quote for new discs/pads if the deem that the current ones will not last until the next scheduled service. And with service schedules on modern cars seriously stretched, that means that even discs/pads that have quite some life left in them will be recommended for renewal.
2. 38k does not say much... brakes are like clutches, their life depends on the way they are used and not on mileage. My elderly father gets 100k out of his clutch, my wife gets around 20k. But my father does motorway driving while my wife does the school run... with traffic lights and speed bumps everywhere. So I don't think you can conclude much from this figure alone without knowing how the car has been driven.
3. Said that, it only implies that from the information provided in the post it is not possible to tell that the dealer was dishonest. But it does not necessarily mean that the work was actually needed either... As some of the replies highlight there are quite a few rogue ones out there.
4. In summary I think that if the dealer contacted the car owner, explained the situation, quoted a price, and received approval, he acted according to accepted standards and it will be impossible now to prove any wrong doing.
Hope this helps....