I'm very confused. In order to use the affiliate link, you actually have to click a box. If you didn't click the box, you aren't part of it.

Medium isn't doing anything that any other writing site isn't doing. I've written for Hubpages for years. When I initially joined 11 years ago, you earned by people signing up through your link. And then you earned a percentage of what they were earning.

Many of the sites that writers here encourage you to join are affiliate links. They are earning a commission on it when you join that site.