Anecdata: I recently shared a private FB event link with a friend over WhatsApp (DM, not group chat) while we were in the same room. She saw and opened it. Some hours later it was gone from both of our chat histories on all devices, with no notice of deleted messages. Earlier and later messages were intact.
I don't see how this could happen if that claim was true.
I don't see how this could happen if that claim was true.