What is meant by "a man prayed over a deceased and was not commanded," and who commands the prayer over the deceased for it to be accepted?

The aforementioned hadith in Ibn Khuzaymah's book, narrated by At-Tabarani from Ata bin Dinar Al-Hudhali, states that there are three from whom prayer is not accepted and does not ascend to heaven: "A man who leads a people in prayer while they dislike him, a man who prays over a funeral without being commanded, and a woman whose husband calls her at night, and she refuses him." The meaning of "a man who prays over a funeral without being commanded" refers to someone who leads the funeral prayer as an imam without the permission of the deceased's guardians, because this infringes upon the right of guardianship belonging to the deceased's family.