First of all, I love that this prompted you to create an account. The author of the parent comment might not care as much if it is on Instagram, because one doesn't give away just as much information there, compared to facebook; and there's no equivalent to the "Like" button that tracks you across third-party websites.

Actually the comment was first posted by a non-green account, then removed and the same comment was posted by this green account.

It's the same company, they own all the domains. If you're using Instagram than FB knows who you are.

Creating that throwaway account was a genuinely good idea...