There is nothing in the drive that would CRACK the disc, Scratch?  Possibly.  I have cracked a disc once pulling it out of the case, while pushing down on the center button where the hub is.  It was stubborn and just would not release, I was bending it, then CRACK.  I returned it and, as it came that way, right?  Xbox360s scratch discs when you move the unit while they're spinning, but never broken them like that.  The clamping mechanism cannot do that, because you are only mating one surface to the disc, there is no bending or stress put on the disc in any way. 

Maybe someone else did it, and just put it back in and did not, and will not admit to it.   

I would not blame the PS3, there is no way it can physically crack the plastic, all the way through, like that.  If it were a SCRATCH, I might even say, it can happen, but a fracture?  No way...

How do you KNOW, for sure, as in 100%, no one touched your PS3?  No siblings?

I just don't see the machine fracturing the disc like that...  Unless; these are slot loaders, and maybe one side hung up while ejecting, and pulled/warped the disc, but if you saw it come out nice and smooth, that wouldn't be it either.  The hub would would also have to hang-up, meaning, it didn't unclamp before the disc was being pulled out...  You would have heard that though...

It's a mystery it seems, ever EVER have I had a disc fracture IN the drive, except a portable CD player when I punched the player on its top, the disc fractured like that...