Holding tank 2/3rd full -- meaning of?

I have a recently purchased 1999 3023, which I have not yet used. The previous owner had filled the system with antifreeze, which I have purged. As part of the antifreeze purge, I added bleach to the fresh water tank to sanitize the system. I also hooked up to the city water connection to see if there were any leaks and to help flush out any residual antifreeze and to purge air from the lines. After disconnecting from the city water connection, I checked the status board (under the sink) which shows fresh water level of 1/3 which is probably the amount I added together with bleach, but holding tank 2/3 full. Why would the holding tank be showing 2/3 full?