Unless there's some explicit condemnation, I would just assume that "this was on HN before" with a link is just a helpful pointer to more interesting comments.
The conventional HN form is neutral, something along the lines of "Previous HN discussion: <link>."
In American conversational English "this was discussed like a year ago" carries the connotation that another discussion is redundant. It reads in the voice of a teenager's critique.
Just wanted to remark the time period in which it was published before, to give some context. I'm not a native English speaker, so excuse me for the phrasing mishap.
