I just finished watching this episode and i cannot help but notice the failure of the final test.

It's pretty obvious that the rocket engine casing failed, which explains the fire coming from the top of the rocket almost immediately after take off.

From studying the video, we never saw Tory or Grant make a weld or any attempt at properly sealing the top of the engine casing (It was simply bolted down).

I think one or more of the bolts failed causing the top to pop off at an angle. This would also explain the secondary exhaust jet from the side of the rocket during the test (As it then technically had two rocket nozzles from the popped top) There was also the big gaping hole in the side of the rocket at the end of the experiment.

Although i think the myth was nothing more than a myth. I do believe without this failure the rocket would of been able to reach the 200m mark before going off course. The parachute system may have also worked from this height.