It means the legal system is investigating the matter and the public prosecutor may or may not decide to file charges. The publishers might have filed a lawsuit themselves, but that is very expensive so they hope the legal system will do it for them. My guess is that the investigation will be closed because I don't think Swedish authorities think they have jurisdiction over Facebook. Unless Meta happens to have offices in Sweden, which I don't think they have. In general they can only prosecute crimes committed in Sweden or committed by Swedes.