Yeah, that would be really nice to get referrals without even using the link, but that isn't the case. The only case that happens is when they opt to subscribe and then Medium asks them if they wanna become members too. Should they opt in, you get the extra dollhairs. It's stated on their page too: https://help.medium.com/hc/en-us/articles/4405927192215-About-referred-memberships

It would be pretty hard to keep track of who gets the money otherwise. Imagine people deciding to convert to member on some random page they just happened to be on after their 3rd article. It would not be a fair system. There are also other pages that aren't author specific. If the system would work the way many assume here it does, we'd all be rich! I bet I'd be raking in 500+ bucks a month from memberships alone. Instead, I rake in just $50+. 🙂