Could have been caused by a number of things. Debris, improper inflation, faulty manufacturing process, etc. etc. etc.
My friend has about 7K on his pr3s and they have been performing very well for him. They feather out quite a bit, probably due to the amount of tread cuts. But he says he hasn't had any handling or very unusual wear issues.
If the posting was correct and he didn't hit some debris, I would guess that it was a manufacturing issue. Thousands and thousands of these tires have probably been sold and worn through already so I would have no reservations about putting them on my bike.