This doesn't happen in practice. Like most marketplaces they have an incentive to market things that are popular or appear to be trending. That means in order for Medium to promote your article you need to do the marketing with your own audience or outlets to get eyeballs on the article and after Medium flags your article as popular it might get promoted.
This is a really big concept because it means if you're just starting off with no audience you might as well grow your own audience on your platform because most marketplaces like Medium (and others) aren't heavily promoting folks with no prior audience.
I remember putting some of my blog posts on Medium and setting the canonical URL back to my site. Out of the hundreds of thousands of visits my personal blog got I only had a few hundred total hits on Medium. That's because I didn't promote and drive my own traffic to Medium and in turn they didn't promote me.