I wouldn't blame your reader; Medium only puts the RSS tag on the main blog page (https://medium.com/@steve.yegge) and not on each post, which is IMO not a good practice.
You are right, I would have to be asking the reader to special case medium or search up the path from the post. In this case it is Feedly which is excellent and does special case the xkcd alt text so I was a little surprised they didn’t do the dirty work.
I went through this same process. Registered for Medium... googled on Bing how to subscribe to RSS, and then added the feed to my reader and logged back out of Medium.