I think you are confused by the English sentence instead (but a similar situation exists in French language as I am going to highlight it later on):

Curiosity is a good quality

In French, we can also say: La curiosité est une bonne qualité. The adjective bonne here reinforces the positive meaning of qualité (in the this context, qualité means good side). Note that you can also understand it (always in this context) as a charateristic/feautre.

But the meaning of qualité may change depending on the context:

1. qualité may be the synonym of good side/good point/advantage (the opposite of flaw/drawback) such as in:

   • Au cours de l’entretien, on m’a demandé de citer mes principaux défauts et mes principales qualités : During the interiew, I have been asked to list my main drawbacks and advantages.

2. qualité may also mean quality, such as in:

   • J’ai acheté des légumes verts de mauvaise qualité: I have bought low quality green vegetables
   • Pour mon anniversaire, il m’a offert un parfum de haute qualité: For my birthday, he gave me a high quality perfume.

“quality” can be a positive thing or just a characteristics, but
indeed this double meaning in French is exactly the same in English !
see:
http://dictionary.reference.com/browse/quality
http://www.oxforddictionaries.com/definition/english/quality