Natural gas is mostly methane but the gas used in vehicles is a mixture of propane and butane. One important difference is their boiling points.
Liquid Natural gas has a low boiling point and is held cryogenically. The pressure required to keep it as a liquid at room temperature would be far too high to be practical. LNG is kept cold on ships by self refrigeration. Some is evaporated, chilling the remaining liquid. The evaporated gas is used in the ship's engines.
Propane has a much higher boiling point and can easily be kept liquid at room temperature in a strong steel cylinder. Butane's boiling point is higher again and can be kept liquid in a relatively weak container. Butane is used in lighters.
The other important factor is the amount of oxygen used in combustion. Many people have died from mistakenly using natural gas equipment on bottled gas. The burner is starved of oxygen producing large quanties of poisonous carbon monoxide.
The most famous case is probably Weird Al Yankovic's parents.