Static pressure is not about fluid dynamics. The name comes from how it is measured. You block the outflow of the fan (for example with a blocked pipe) and meas

Static pressure is not about fluid dynamics. The name comes from how it is measured. You block the outflow of the fan (for example with a blocked pipe) and measure the pressure difference between inside and outside of the pipe, while the air is static (ie. it does not effectively flow through the fan). The pressure difference caused by the fan will be different from the same fan but running in free air (not obstructed).