The meaning of 'oh sure'

Hello everyone. I have a question. What does 'oh sure' mean? 

This morning I had a conversation with my friend. I asked him if he still has fantasies about me/ interested in me. He answered 'oh sure'. He always replied to my requests and questions with 'sure'. 

Is there a difference between 'sure' and 'oh sure'? I believe that 'oh sure' implies a sarcastic tone in the message. Is that correct?

Please correct me if I am wrong.

Thank you and have a nice evening! Blush