I don't think they're saying the word fetch means irrelevance. They're saying fetch is something irrelevant. :)
No, they're claiming that "fetch" is interchangeable with "irrelevant" according to the movie.
This is clearly not stating that the actions by both parties are "irrelevant", it's clearly slang for "cool" or "awesome". The movie was alluding to the word itself being irrelevant in its use, not the word meaning or being synonymous with "irrelevant". I hope this cleared things up for you.