The citation for these records says that they are from the Dutch Reformed Church Archives, Potchefstroom. They are baptisms from 1915-1971, however, they are not only from Lusaka and it is not always clear where the baptism took place. Other places that are mentioned are Mufulira, Luanshya, Broken Hill, Krugersdorp, Livingstone, Kalomo, Bowwood, Chingola, Nkana, Zimba, Bulawayo, Chomo, Pioneers' Rest, and Tara. Some names seem to have come from registers in Rustenburg, in the North West province of South Africa.
Image 21 in the FamilySearch records includes some duplicated records from the begining of the register as well as some baptisms that are not mentioned earlier, but also have no dates attached to them.
See the full list of names here!