There's a difference between actual plies, and Ply-ratings.
You have 2 Polyester plies in the sidewalls.
In the tread area you have 2 Polyester plies, 2 Steel plies, and 1 Nylon ply.
A C load range is in an LT (Light Truck) tire. You have a P (passenger) rated tire, which would be given a 4-ply rating.
A C load rating has a 6-ply rating.
A D load rating has an 8-ply rating
A E load rating has a 10-ply rating.
A F load rating has a 12-ply rating.
Etc, etc.