"Now, we count a read when someone views your story for 30 seconds or more–scrolling to the bottom of the story is no longer required. For this reason, you will likely find that the “reads” and “read ratio” numbers are higher on the new Stats pages than they were previously."

Thought this would help, quote from this entry here:

https://blog.medium.com/partner-program-updates-part-ii-stats-edition-194ddd7c016c