I have a couple of questions. Your scenario that you outlined in your message could have been a part failure or one of several other scenarios.

Was the bolt holding the seat over tightended or slightly loose? As either of these situations could cause undue stress on the bolt.

Was this a Ti bolt, as over tightended Ti bolts will stretch. I know from experience and have since gotten a torque wrench.

Have you bunny hopped anything and have come down hard on the seat?

Has the bike been crashed and the seat hit the pavement?

Was the clamp in the middle of the rails? If not then cantilevering the seat over the post would also cause undue stress on the rails and the bolt

If no to all of the above, then you would have a part failure.