This probably happens because these links aren't paywalled for everyone. I, for instance, have never encountered any paywall on any medium.com article; whether

This probably happens because these links aren't paywalled for everyone. I, for instance, have never encountered any paywall on any medium.com article; whether that is because I have my browser configured to discard all cookies whenever the browser is closed (and I close my browser very often), or because I have it configured to disable Javascript by default unless the site is whitelisted (and medium.com is not on the whitelist), or something else, I don't know.