The guy obviously chose acetylene because it creates the biggest bang .... acetylene has the highest energy of oxidation of any gas , this enables the resulting burnt gas products to be very hot =bright light = high pressure =big bang
2 molecules of acetylene combine with 5 molecules of Oxygen ... so that's the volume ratio required for complete combustion ...
2 liters of acetylene with 5 liters of Oxygen
Since the fire ball will mix with the oxygen in the air , and can burn with some of this oxygen , err slightly on the rich side , perhaps 2.5 +5 ..or 1:2 ....
One liter of Acetylene mixed with Two liters of Oxygen
They had 1,500 liters of gas in the balloon .. that's around 2kg .... the explosion would be approximately equivalent to the same mass of TNT or dynamite!
Let me just check I'm correct .... from search " 1 gram of TNT is approximately 4K Joules. "
Also ..... " burning 1 mole of acetylene will release 1253.3 kJ of energy.
C2H2 ..... one mole = 26gm 2 moles is 52gm and this needs 5 moles O2 = 160gm so 2 moles of acet plus oxogen weights 212gms
1 mol +oxygen weighs 106 gms and produces 1253KJ ........12KJ per gram .... TNT is only 4KJ/gram
So the gas mix is around 3 times more explosive than the same mass of TNT ... Although TNT starts from a solid which create higher peak pressure if very close.
The energy released by hydrogen and oxygen is just slightly higher per gram(13.3) than acetylene and oxygen (12)
But this is all about how much mass you can get into a balloon ... and Hydrogen Oxygen are a third the density , so would give an explosion 30% as intense as Acetylene Oxygen for the same size balloon.