> ...you can't control what others send you.

Of course not. You can, however, control what you then do with said data.

If a courier accidentally dropped a folder full of nuclear secrets in your mailbox, I promise you that if you do anything with it other than call the FBI (in the US), you will be in trouble.

Except in this case it's unclear whether any intentional decision went on at meta. A better analogy would be if someone sent you a bunch of CSAM, it went to your spam folder, but then because you have backups enabled the CSAM got replicated to 3 different servers across state lines, and the FBI is charging you with "distributing" CSAM.