bUchi was used to mean "bhUam". It is not derived from it.
Its etymology, however, is most likely, what you suggested:
"'pooci', in tamil means worm, or insect. That could be
the origin of booci in telugu." In Kannada too, 'pooci'is a worm. DED gives
these words as cognates, though it does not mention bUchi.
Etymolgies are often difficult to prove. Especially in a culture where a lot of
languauage does not get recorded. So I would not argue with people who want to
derive bUchi from the French general Bussy. All I can say is that it is not very
likely.
Also I wonder why we are bringing Portugese in. Bussy is French.
VNR