It can happen to shotguns. Ever heard of a 12/20 burst? Someone mixes the ammo and loads a 20 along with the 12s. The 20 slips into the barrel and the following 12 blows the gun. It can also happen with slugs, mud and wasp nests.
I am guessing obstruction from the way the barrel and slide look. No bulge at the split so it is a hard call. It looks like the slide did not have time to travel so it was pretty sudden. The slide and frame contained it so there was no major shrapnel flying as there would have been on a revolver.
"I would not be an old man if I had not been an armed young man." JTJ
Patron Member NRA
"As democracy is perfected, the office of President represents, more and more closely, the inner soul of the people. On some great and glorious day the plain folks of the land will reach their heart's desire at last and the White House will be occupied by a downright fool and complete narcissistic moron."
--- H.L. Mencken, The Baltimore Evening Sun, July 26, 1920