Internal controls (Key controls to place reliance)

"Employee hours are preset into the payroll system with all the necessary deductions. The payroll manager takes a sample out and confirms the accuracy of the net pay" The question states to find the key controls to place reliance I came up with two key controls from this statement which were the use of the payroll system which minimises the risk of human error and the other being the payroll manager confirming the accuracy whereas the answer just puts emphasis on the payroll manager confirmation So, is the payroll system not a key control to place reliance on?