You're probably very luck it broke when it did. I'm guessing the higher you would have gone the more likely in might have ended up in the ocean.
Maybe a good way to do an inspection of the props is using a flashlight. Shining a light on each prop may reveal a micro crack that wouldn't normally be visible.
It would be interesting to know if Parrot has a recommended number of flight hours for replacing the props. That said conditions that might introduce nicks or scratches (landing and taking off from sand or dirt) may be more of a factor versus flight hours only.
