I believe it's industrial protocols used to connect such devises to a SCADA system. It this case it's the SCADA system that has to be disconnected from any general purpose networks.
The freezer itself doesn't need to connect to a SCADA. You can network power and temperature monitors, but those monitors don't need the ability to shut off the freezer.
These freezers are manually stocked and cleaned. If they need to be powered down it's a simple matter of a hardware switch that you flip when the unit is empty.