Helpful video: https://www.youtube.com/watch?v=Kyc_ysVgBMs
But basically, the picture was a cropped frame from a CSAM content, which then their systems thought you are posting CSAM content when you did not.
About the legal consequences, i am not a lawyer, but i don't think you will be visited by the police anytime soon, since the picture you posted isn't CSAM by itself, just a cropped portion which does not contain the material itself.
Edit: as someone said, it goes through multiple human reviews.
Can we get a permanent outage of that goddamned website, pretty please? For the sake of humanity?
There have been so many instances where i wanna see replies of a post or more stuff about a person, but then that mandatory account log in wall kicks in.