That is a very narrow definition of freedom. For a simple example of freedom being taken away without state involvement: a person who (illegally) locks up another person is absolutely taking away another person's freedom.

This idea that only freedom from the state counts is very pernicious, and it's at the root of the inordinate power corporations have in today's world.

Freedom is the ability to do what you want. Any conditions that don't let you do what you want are restraints on your freedom, even if they are being enforced by a private company.