Wow how did you find that? I does make sense in a way, as far more countries use 220 and 230 volts. Japan almost alone in using 200. They also install mainly 3.3 Kw chargers in the JDM cars. 29 amps at those two voltages (220 and 230) are right around 6.6 input.
The manual doesn't tell how any of the components in the charger function. There is something they call "power factor correction" (their term not mine) after the initial rectifier, and before the inverter. My guess is the inverter is where the current limiting is done. By rectifying 1st, before anything else, it makes input frequency moot.
Like most modern manuals they don't explain the how or even the why, only how to test/replace.
edit:
I never doubted it could set the amps, just if the max input in Kw was determined by current regadless of input voltage or only the max Kw the charger can see is determined by voltage alone. From what I can see on the report neither is 100% true. It can take more current at lower voltages than 240 to bring the input Kw more in line to the stated input capacity of the charger. While there is some "wiggle room" you couldn't feed 60 amps of 120 volt into the input and get 6 Kw on the charger.(Obviously).