For the fire the source of energy is the "chemical" energy stored in the reacting compounds whereas for lightning the stored of energy is electrostatic in nature due to the separation of charges.  

Comparing power, [gas fire](https://physics.stackexchange.com/questions/194367/how-big-is-a-1kw-fire) - $2\times 10^4$ watts and [lightning strike](https://www.weather.gov/safety/lightning-power) - $3\times 10^8$ volts and $3\times 10^4$ amps $\Rightarrow \approx 10^{13}$ watts, you will note that the rate at which energy is dissipated in a lightning strike is much, much greater than that in a gas fire.  
Thus one would expect the lightning strike to last for a much shorter period of time than that for a chemical fire.