Buccaneer comes from French boucanier, a woodsman or pirate in the seventeenth-century West Indies. Behind it is boucaner, to smoke meat, from boucan, a wooden smoking frame.
The omitted French person noun boucanier connects meat smoking with West Indian woodsmen and pirates. English is already recorded with the pirate sense; the deeper Tupi formation is outside these slots.
Source
Merriam-Webster: buccaneerWord History gives boucanier, boucaner and boucan, then the deeper Tupi formation; the first English use is already the pirate sense.