Nodal boundary condition

Hi experts,

Could you please explain the significance of nodal boundary condition on a single node only? I have grabbed the following picture from acusolve validation manual.

https://help.altair.com/hwcfdsolvers/acusolve/topics/acusolve/turbulent_flow_through_a_pipe.htm

When I checked the model, I could see that there's fixed pressure only at a single node 8908. How does this work?