I have had this same thing happen. It wasn't on a post that was as expansive as you mention, it was just a review on a cannabis extract, but the user flagged it simply because they did not like it even though it was completely original content.
Nothing followed my last question
This user was a dolphin and caused my post to immediately go invisible. I've been thinking of making a post about abusing the flag option after talking with the person who flagged me for just not liking my post.
RE: So I got flagged for my birthday...what did you get? (Plagiarism the plague of all time)