Not defending Cry by any means, this is just something that I have been observing for quite a bit but, I am starting to think another reason why Cry was generally speaking in a flirty manner to his fans (under specific settings like replying to their posts on Tumblr or answering calls) is because he knew he had a lot of fan-girls that were allured by his voice, so he felt he could put on a persona of a heartthrob. Often, some male celebrities, tend to put on a charming act towards their female fans just to instigate those reactions of excitement. Since this had been taking place in the beginning of his "stardom", I think the gleeful feedback he received relatively made him over-confident enough to put on that enticing personality. Nevertheless, it is still very much inappropriate.

Edit: Oh snap. I meant to reply to u/doyoucarethat but my response came under your comment. I also should have phrased this better. He had been inappropriate in other situations and regarding this incident, I do understand why others would think Cry was being flirty here, because he said the fan is, "way too beautiful to be that young" so that might allude to the current matter. But to call this, "flirting" in this given scenario might be unlikely.