If your gas is compressing itself, it’s creating a high-pressure environment in your, err, guts. That means it’s creating a lower-pressure area outside - i.e. you are sucking gas in to compress it.

Farting or belching - i.e. ‘gas’ in American - is rapid /decompression/, not compression.

(In practice, I think it’s rather more a case of gas is /created/ by biological means, i.e. it is not ‘compressing’ anything per se.)

It’s possible that you suck more for not being able to take a joke, though.