I'd assume that they're taking a word count and then using a predefined number of words per minute to figure out approximately how long the article will take to read.
For example, https://medium.com/fragmented-musings/295cc75cd1fd has approximately 600 words and has an approximate reading time of 3 minutes. From this we can deduce that they're assuming that around 200 words can be read in a minute. By diving 600 by 200, we arrive at 3.
For example, https://medium.com/fragmented-musings/295cc75cd1fd has approximately 600 words and has an approximate reading time of 3 minutes. From this we can deduce that they're assuming that around 200 words can be read in a minute. By diving 600 by 200, we arrive at 3.