"heavy" instead of "big" has not been accepted
It should be 'heavy' indeed, big would be 'kubwa'
If heavy means nzito then why is it accepted in this particular context?
Maybe it's because that's what the English phrase is? A lot of idioms don't translate directly but have an equivalent in other languages, so the Swahili could very well be "He has heavy bones" and it's just not directly translated in English.
In English, "I have heavy bones" means "I am fat." If someone told me, "I have heavy bones," it would mean, "I am tired."
so it it 'tired' or 'fat' in English? And what do they imply in Swahili in this saying?
Big-boned / [Someone has] big bones = Fat
Heavy bones = Tired
We're assuming that even though the literal translation is "heavy bones," since Duo's official translation is "big bones," that this phrase is equivalent to the English idiom meaning someone is fat.
Mifipu os short not big so he has small bones.