It's just CG...

Its been bothering me for a while but every time I read a manga that has normal people in it but unnatural or unrealistic things, they always dismiss it and say "Is it CG?" I'm pretty sure CG is NOT something one can see irl at the actual set of a scene say if it really was a movie scene (but its not). So why to people in mangas and anime always dismiss these events as CG?

You pretty much don't get the joke then >_>

This looks like it would be more appropriate for random. But ya it's just something that is used for humor...