Your system has a TXV for its metering device. The correct charge is determined by subcooling. The superheat still needs to be checked to verify that there are not other refrigerant circuit related problems though.
Depending on the model, your system has 1 or 2 factory installed liquid line filter driers inside the unit, there should not be one installed outside the unit.
Many people charge a system with the refrigerant bottle turned upside down, and either throttle the refrigerant in with the valve on the refrigerant manifold, or use a small device that goes inline with a refrigerant hose that insures the liquid flashes off before it makes it to the system.
You walked up behind a guy, who had his attention focused on something else, and you are concerned that he was startled when you said something?
I do understand your concerns though.
Only a very small percentage of installers and service techs actually flow nitrogen through a system when brazing the refrigerant lines. This despite it being a specific requirement in virtually every manufacturers installation instructions.
Only a minority of installers/techs who actually use a micron gauge during evacuation, again, this is despite clear manufacturers instructions regarding vacuum level requirements.
Depending on who's study you look at, between 56% and 73% of newly installed systems are incorrectly charged at startup, most by more than 10%.