Wikipedia goes into far more detail about the technical definition of irony than I care to, but I believe the important part is that a statement is ironic when

Wikipedia goes into far more detail about the technical definition of irony than I care to, but I believe the important part is that a statement is ironic when speaker's words have a relevance to the situation that the speaker is unaware of. I'm assuming that nobody could read HN for very long and remain unaware that the site is targeted at programmers and entrepreneurs. Because the author of the original blog post knew the purpose of HN, he would have recognised the incongruity between his statement (that coding and startup articles be filtered out) and the reality (that HN is all about coding and startup articles). Since he was aware of the disparity, and irony requires unawareness, there was no irony. I'd have given you "sarcasm" or "incongruity", but "irony" is one of those topics that triggers my "Someone Is Wrong On The Internet" reflex, I'm afraid.