If she was smiling and looking at you in the eyes when she said this then it was an IOI, meaning your response needs to be an IOI. If she was looking at you weirdly and gone off when she asked you this then its an IOD so you must reply with an IOD.

As for your reply something i think is always good and flirtatious is to reply to a question with another question. You can flip the question back onto her if your not sure of the best reply.

"well do you always go up to guys youve never met before?"

AJay