You're conflating openness with equality. Public salaries don't mean they have to be the same salary for all, because people are not the same.
It's frequent that the salary of a freelancer working for a company becomes public among its employees. That doesn't mean similar employees will ask the same salary, because they know the freelancer can do something they can't, or they can't do it as well.
Or more literally, you can't take a freelancer on a 3 month contract at 700 a day and say, "well based on what they're being paid, my salary should be 170k!"
It's frequent that the salary of a freelancer working for a company becomes public among its employees. That doesn't mean similar employees will ask the same salary, because they know the freelancer can do something they can't, or they can't do it as well.