If you aren’t a part of the partner program, then your posts are not behind the paywall (because you are not eligable to put them behind the paywall). Any posts you, as the author, have not flagged as members-only are free to everyone.
And, of course authors are not immune to the existing monetization system (any moreso than journalists see no advertisements in magazines). Medium as a platform makes no distinction between authors & other registered users.
There are problems with Medium’s platform & the way they are handling their paywall system, but factually-inaccurate articles like this don’t help.