BBM.....I woud "think" (though I don't KNOW) they're taking into account "huntable" (by any other account) sq. mi. tracts.....whether hunting is actually "allowed" there, or not.
For every instance of the numbers you cite.....you probably have THOUSANDS of sq. mi. of land that is otherwise legally "huntable"....but no one has permission to hunt.
That's just my thinking, though.
In my area, thats not even close to being accurate.
Edit** - BBM I missed that statement, earlier. Your observations only ADD to the density issue. I don't doubt YOUR scenario is likely MORE the "norm" in PA, from what I've heard.