I'm not so optimistic these days. Poe's Law has long since died. Even if this was misunderstood sarcasm, you can probably find this opinion around the net (mayeb even further down the post).

One thing that's doable on HN is checking poster's previous responses/history to form a better idea.

Unless I'm daft, I'm not seeing sarcasm in their more recent comment history, nor do I see it in their post here.