I think yes.
And the reason is that - grammatically correctly - ‘gu dona’ is an adverb.
The answer part is effectively short for saying ‘I’m not doing badly’.
Or ‘not badly’.
Gu + dona = badly.
It’s English that is irregular and hence your question:
In English, rather than using a grammatically regular adverb (badly), we use an adjective instead (bad), ie we say ‘I’m not doing bad’ or ‘not bad’.
Also applies with good/well. In standard British or Scottish English we’ve have tended to say “I’m well’ and it’s only comparatively recently that the US English ‘I’m good’ has crept in.