Relatively new tube exploded by itself without any external force
A bang explode pretty much only happens when the tube leaks out from tire.   

Either the slit is big enough for the tube to push through or the tire pushed over the rim and the tube leaks out.  Without a tire a tube will only handle a few pounds of pressure. I suspect the tire belt is damaged.  When you see the tire off the rim you might assume the explosion blew the tire off the rim but most likely the tire came off the rim and then the tube exploded.