Is curiosity, for non Dhamma subjects, a bad thing?
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.