A person can have flashbacks related to an original trauma (often forgotten/supressed/frozen etc) but transfered to other people and situations (Trauma Transference Syndrome). A person can be abused/traumatized and lock the menory away, and then an innocent person can benignly cause the buried trauma to emerge. The innocent person can then be seen as the original perpetrator. In that sense "flashbacks" of things that didn't quite happen (as re-experienced) can happen.
Oh there's also vicarious trauma where counselors, therapists and others can experience the traumas of others. Flashbacks and intrusive thoughts can come from that too. People can show effects from traumas of others they get involved with.