It is boost pressure in the sense that the air going into the intake manifold is above ambient pressure. It isn't like nitrous where air still comes in the inta

It is boost pressure in the sense that the air going into the intake manifold is above ambient pressure. It isn't like nitrous where air still comes in the intake, with compressed air systems there is a valve that's closed to prevent the engine from ingesting ambient air, it runs entirely on the compressed air.