With a glass delam, I would have concerns.
There are several reasons that this could happen,however if there were no outward signs of abuse, and the overall condition of the bow shows due care and diligence, I would have to throw a manufacturing issue into the mix.
I wouldn't expect the bowyer to eat the entire cost, but a substantial discount, and go to the top of the list should be in order.
The owner showed little class, and not something a trad ganger would do. He also has to take into concideration that he has been using the bow for 15 months, and therefore it is used, whether he abused it or not.
These custom bows are expensive, and are probably going to get even more so as time goes on, I can see his frustration, but he needs to take a look at it from the bowyers side of the page.