External views are often when someone accesses your story via a web search. Google, Bing, etc.
Views on Medium are simply when someone clicks on your story. If they read the entire story the View also becomes a Read. A View can be an accident. LOL.
Reads are better than views if you want people to read your stories. But since Medium now pays by read time, views are the focus. A person can read half your story and stop. You still get a View and credit for the time they spent reading half of it. But not a Read.
That is how I think it works. You never really know for sure with Medium.