I had a very similar incident. But it was a 26" X 1-3/8th inch tube made under the name Inline. It was a brand-new wheel I'd just trued, with a brand-new Panaracer tire on it. I had also put on a Velox tire-strap in 22mm. There was nothing sharp in the brand-new tire or rim, and the tube blew up. I'd pumped it up to 55psi. Set it aside. And BANG!! It sounded like a 9mm handgun (I'm a gun nut).

I removed the tire and tube. It blew-up in the direction of the outside of the tire, and a couple of inches away from the valve - the valve had escaped the blast. And it was a 4" to 5" inch-long gash of jagged rubber. Never had that happen before.