This birbs name ended up not being luffy. Its ruferu/ruffle (according to the wikia). Luffy was a mistranslation.

genshinimpact said:
This birbs name ended up not being luffy. Its ruferu/ruffle (according to the wikia). Luffy was a mistranslation.

It's uncertain. While "Luffy" has been wrong from day 1, in Japanese his name is given as ルフェル (ru fe ru), in Chinese it's 路菲尔 (Lu fei er), and you can additionally compare to ルシフェル (ru shi fe ru, "Lucifer") and 路西菲尔 (Lu xi fei er, "Lucifer").
The only truly authoritative name we have right now is the codename "Cattle", but this might change as the game is formally released, or as it becomes available in other languages (whether officially or by a fan project.)