Did you chose more than one university after you have submitted your offer letter during the application exercise. If yes, the secretariat wants to be sure of your choice that why you receive another update as a semi finalist. Because should you have chosen just one University, they would have only updated you as a finalist and not a semi finalist.
For those of us that chose one or two courses from one university, there is high tendency that we would not receive message in May but shortlisted as a finalist in June or early July.