It's obviously a rejection, but not obviously for the reason stated. From his point of view, he's just received a forward of an "open letter" that some blogger

It's obviously a rejection, but not obviously for the reason stated. From his point of view, he's just received a forward of an "open letter" that some blogger he's never heard of has already published seeking to gather attention at his expense. My guess is that he really wanted to write "Who are you? Go fuck yourself" but thought better of it, and this was really the only point he could score given how little he knows about the blogger.