This phrase goes back to the period of exploration of the British. When the British discovered America, their sailors would come back with foreign artefacts, crafts, goods, etc. and these were referred to as far-fetched i.e. being fetched from afar.

What does the saying far fetched mean?

1 : brought from a remote time or place. 2 : not easily or naturally deduced or introduced : improbable a far-fetched story. Other Words from far-fetched Synonyms & Antonyms Learn More About far-fetched.

What is Farfetch based on?

The story behind Farfetch'd is that of the legend of a duck, who fetches a green onion for a person, only to bring it back to be cooked with the leek himself. The Japanese name is a further play on this; "Kamonegi" is a portmanteau of 鴨 kamo (wild duck, but can also mean a gullible person) and 葱 negi (a type of leek).