Pretty sure the laser did not burst into flames, rather the methane in the fart.
Journalists. Geesh.
One source says:
A typical breakdown of the chemical composition of farts is:
Nitrogen: 20-90%
Hydrogen: 0-50% (flammable)
Carbon dioxide: 10-30%
Oxygen: 0-10%
Methane: 0-10% (flammable)