Mina smiled a bit as she saw his smirk. He seemed like a person that didn't have a lot of fun, even though he wanted to. She felt comfortable in his presence and even found talking to him a fun thing to do.
When he answered her question so hesitantly she wondered why he sounded so hesitant. He worried about her, that would mean he did see her as a likeable person to some degree. 
'If you have somewhere to be you can go if you really want to.' she added to her question.