A split barrel is almost always due to a bore obstruction of some sort. Like SGB, it looks to me like there was an obstruction of some sort at or near the muzzle. A case letting go will usually vent down the mag well, blowing out the mag and often splitting the grips as well. Were you able to find the empty case of the round fired when this happened? Did you, perhaps have a malfunction that you cleared manually immediately prior to this happening? Were you shooting more than one caliber of handgun that night? In particular, were you, or anyone else with you shooting a .40 also?
Is the entire barrel split from the chamber forward or just part of it...maybe toward the muzzle?
I am not accusing you of not telling the truth, please realize that, I just know from experience that things can get fuzzy in our memory when something like this happens. The event itself sort of makes whatever preceeded it unimportant to the memory, but often the preceeding event may be the cause.
If you still have the ammo you were using do NOT get rid of it! For sure, WW will want to take a look at it.
Good Luck, and I am glad you were not injured.