I think that she is just extremely possesive person. She doesn't like MC, but also doesn't like that there is possibly other girl that 'has' him. So she wants to confine him with words like that. I mean he confessed to her and asked her to go to his house after a date, she responded that she has a boyfriend. But now she says that she likes him. It's not let's go out together, but 'I like you and I know that you like me so stay away from other girls in case I decide to go out with you'. Then again, let's see what will happen in next chapter cause all my rumbling can go down the drain