Ok, so...
If this is an adaptation or something I have no idea, this is just my personal theory:
I think the fan is an ex-male idol, and thus he can see and appreciate the parts of her most of her fans would not notice.
Not only from the glimpses of his face under the glasses that seem to show he is good-looking like those are usually drawn, but also his constructive criticisms that shows he does know how a good idol should act, plus how he appreciates the most when she acts more natural instead as idol-like even is most of the time those are blunders.