I don't think you want to try that argument with immigration officials, although it might just keep your incorrect answer from being straight up fraud or willful misrepresentation.

I mean, some US govt immigration forms asking for your social media usernames include pastebin sites like "justpaste.it". See for example: https://static.feber.se/article_images/42/10/92/421092_1280....

Knowing that, it's crystal clear HN falls strictly within that definition of "social media", although it might not be as clear if you don't know what that particular site is.