My understanding is that internal and external referrals just indicate where the reader came from. Once they get there, if they are a Medium member you get paid, if they are not a Medium member you don't get paid. So, I don't think you lost any money. The responses don't seem to clarify that. I believe there is something in the support documents that states that if a Medium member accesses your story through a friend link, you still get paid. You also get paid if they join after reading your article.

Here is the note about the friend link:

Will sharing a Friend Link impact my earnings?

No — if you set your story to earn money through the Partner Program, you’ll continue to earn when subscribing members engage with your work.