I don't know how to react lol...
It is rude indeed, but somehow I feel like this is about the best way they could be blatanly honest. MNET is parent co of CCM, where Jiyeon is housed. And I believe, Jiyeon has passed that stage where she would get much hurt by bypassers' rude comments.
Those won't kill her, and she'll come out stronger and better.
You know, she's Jiyeon.
*I bet some celebs do feel curious of what sort of bad comments would be said about them by people on the streets lol*