You wouldn't have been in true danger unless someone wanted to investigate the smell by lighting a fire.

Nowadays all the gas you can get isn't 'coal gas' or 'water gas', so there's no CO in it.

Gas leaks, that contain CO are from water gas and coal gas, not natural gas, so unless the person lives in a place, that still produces those, they're absolutely fine until someone makes a spark in the gas filled room.