You're misassessing the costs and benefits of attacking people for posting anonymously.
Re costs: Look at https://news.ycombinator.com/posts?id=oceanthrowaway - the odds that this commenter is legit are quite high. Would it would have been better if they had posted under a regular username? Sure, but people sometimes have good reasons for making throwaway accounts to post about topics they're professionally expert in. Such comments add value to HN, sometimes a lot of value (e.g. sometimes they give important inside information about a topic), and punishing people for doing that is against the community interest.
Re benefits: it's not at all easy to "shape public opinion" by an anonymous comment on an internet forum. You'd have to do it repeatedly, and the more repetitive it gets, the more predictable the comments become, and the more likely the community will have an immune response to it. In my experience from moderating this place over the years, internet users are far too quick to assume that they're encountering manipulative stealth behavior.
What you should be responding to instead is the quality of the comments. If a throwaway account is repeatedly posting low-quality comments, then sure, that's a good reason to be critical - but the throwawayness of the account should not be the high-order bit.
If you had made your point less aggressively, I probably wouldn't have responded, but you came down on the GP like a hammer (e.g. "spreading FUD from behind anononymity") and that put your comment on the wrong side of the HN guidelines.
https://news.ycombinator.com/newsguidelines.html