Only two pieces...

to me that indicates some sort of flaw in the spar, be it a scratch or something wrong during manufacture, not a normal overload blowout

Hard to say, I tend to Whump pretty hard.  

Street flying is very hard on gear anyway. Blew out an original diamond (first run) right at the point where the ferrule ended. Had about 2" still on the ferrule and the rest - trashed. Now my diamonds only fly at the beach with the rest of my team on SULs!! It'd need to be pretty bad to use them in any other situation.