I'm always interested to see exactly what is included and excluded from their definition of reading. On average, most adults actually read more today that we did in the 90s, if you're purely talking words of text consumed. Are graphic novels being included in these stats? Short stories? Social media threads? Most people even watch videos/tv/movies with subtitles they read now, which was not something that was an option before.
The actual article text never says the word "book" once, but I strongly suspect that is all that's being counted.