I disagree with that statement.

Private land birds do get pressured because of tresspasser or people hunting a joining properties. And if your privat land boarders public it just may as well be public because those birds are getting called and pushed just as much as the public land birds.

No matter how much homework you do on public land all it takes is people beating you to your spot or they are after the same bird as you. That has happened to me more times than I care to count and as much as 4 or more people are all calling the bird you are hunting. On private ground you don't have to worry about that unless people tresspass.

Public grounds that have alot of hunters is going to be alot harder to haverest a bird from than private ground that has only a few people with permission to be there.