Turbocharging has a great relationship with throttle opening.

Your understanding of turbocharging should be about the same. The function of turbocharger is to increase the intake air. For gasoline engines, the amount of air entering each cycle increases, and the amount of fuel injected increases accordingly, so the work generated by a single cycle also increases. Torque can be regarded as the load of the engine. In order to achieve the same torque, that is, under the same load, the more work a single cycle does, the less time it takes, and the number of working cycles can be reduced, so the speed will decrease.