Is curiosity, for non Dhamma subjects, a bad thing? Curiosity can lead to desire (for knowing something), attachment and therefore suffering. Also, questions based on pure curiosity were left unaswered by the Buddha

On the other hand, curiosity is what makes us evolve, so is it good or bad? How should one sees it?
Asking questions / being inquisitive can lead to intelligence. 

Having said this the quest for knowledge can lead to:


attachments to per suits of no benefit to this life, after life or liberation hence wasting time and effort
attachments to the quest of seeking answers leading to pure study / research or philosophising, this also may not always be time well spent. 


If you are leading a householders life you cannot avoid these always. But your per suits should be fruitful for either:


This life
Next life
Liberation


Beneficial to either:


oneself
others, or
both


If your quest is not profitable best is to leave it a side.