Since natural gas is lighter than air and dissipates rapidly when released it means it's pretty flammable and takes very little to ignite.
So although gasoline is also pretty flammable and can ignite easily as well natural gas is more flammable than gasoline and although gasoline vapors can explode to natural gas can explode more easily than gasoline even with just a flick of a light switch or slight spark.
Gasoline vapors are what ignites and explodes instead of the gasoline itself.