Not necessarily
Like I said, it's possible there was a rupture instead of an explosion. A rupture would vent the gases through it similar to a nozzle. This seems to me more likely than a true explosion, if for no other reason than the volume of the propellant tanks. Those 3rd stage tanks were quite large and built to withstand a fair amount of pressure, so it'd take a lot to overpressurize it with the residual propellants.