Posting "is this satire" is an internet trope, a way of snarkily putting down what someone else said. In that way, it's a provocation and in that way flamebait.

If that explanation doesn't land, there are other site guidelines which maybe make the point more directly, such as "Don't be snarky", "Edit out swipes", and/or "Omit internet tropes".

https://news.ycombinator.com/newsguidelines.html