Praise be to Allah.
This is a kind of death announcement that is permitted. Hence the Prophet (peace and blessings of Allaah be upon him) announced the death of the Negus on the day on which he died. When the woman who used to clean the mosque died and the Sahaabah (may Allaah be pleased with them) buried her and did not inform the Prophet (peace and blessings of Allaah be upon him) of that, he said: “Why did you not inform me?” There is nothing wrong with announcing the death of a person so that more people will attend the funeral prayer, because that is something that was narrated in the Sunnah. But announcing it after the burial is not prescribed, rather that is the kind of death announcement that is forbidden.