He's saying a zone is based on where all the seats are already installed on the plane. Front, middle, back, other than premium seats, and the screamin' baby express passengers. So if you are in row 10 on one flight and row 30 on another you will be in zone 4 and zone 2 on the two different flights. This is how almost every airline in the world boards, whether zones 1,2,3 or A, B, C, or row numbers. To keep people boarding in the front rows blocking all the others from getting past them to the rear of the aircraft.

Everyone's zone is based on the same rules. Your question sounds like they did this only for you.