Not sure their exact method but unless the beer is bottle conditioned to carb up, it is alredy carbed in another vessel and then just transferred into a bottle or keg.
The general adaption for home brewing is to take beer from a keg that is fully carbonated, dropping the pressure input down to a few psi, connecting a tube to the tap faucet and transferrring this beer into the bottle. The counterpressure device allows beer to go into a bottle where the oxygen has been replaced with CO2 and the CO2 gets pushed out as the beer fills the bottle.