(OFF)
No, 'zephyrum' is the right Latinized form of the medieval North-Italian word 'zefiro', witch comes from the Arab 'safira' (='empty', it is the translation of the original Indian 'sunya', used for 'zero' -- what is the Venetian contracted form of 'zefiro', used word-wide today...)
The nominative and accusative of second declension singular neuter nouns have the same -um ending in Latin. Eg. gaudium, auspicium, servitium, auxilium. Also, neuter abstract nouns, names of groups and offices, and neuter foreign words usually have the same nominative and accusative. The word 'zephyrum' was made by Fibonacci himself, who wasn't under-educated in Latin. -- He may have played with the Greek word Zephyros as well, when he brought westward the concept of zero from the Middle-East.
(/OFF)
What he said! ;-)