What does the information "operating hours" under reliability in the data sheet mean?
A value of 8,760 is given there. That corresponds to exactly one year of continuous operation.
This is the recommended number of operating hours of the HDD per year. This means 100% or, as you have already assumed, continuous operation. However, always consider the value in connection with the workload rate of 180TB (for this HDD).
PS: In comparison, a BarraCuda, for example, performs 2400h/year at a workload rate of 55TB.