Yes, you probably trapped enough air in the tank to make it function to some level. I imagine that it was still short cycling to some extent. Because water is not compressible (or at least very nearly not compressible) it takes virtually no leak at all to cause a pump to short cycle. You might not have at leak at all. The only way you can maintain pressure in the system is by actively pumping, having head pressure, or compressing something. When the pump is running, the pump is providing the pressure. In a working system, the compressed air in the tank provides the pressure when the pump is not running. In a municipal water supply, head pressure pressure from a water tower provides the pressure.