You can quite clearly see the crater extends downwards below the pipe. In a similar and proportional way, a larger pipeline explosion would have a larger crater.
You wrote: "did the explosion occur *inside the pipe*? No sir it did not, because, there is no oxygen to cause the gas to be explosive inside the pipe"... I just explained there are multiple causes of pipeline "loss of containment". E.g mechanical failure or operational/human error (internal over pressures). So the answer is possibly yes, it possibly did explode due to the pressure internally exceeding the failing point of the pipe, as evidenced by no "fireball explosion", I think it was quite clearly an internal pressure build up, analogous to an internal pipe explosion.
