It means passively absorbing information can make you dumb because you're not demanding brain power (lack of using a muscle atrophies). Compare scrolling on Facebook to watching Television -- completely passive.
It means that they are adapted to a much higher stimulus level and lose interest if they have seen something beforehand. Also that they are a conceited brat who is convinced that they are the center of the universe. Or at least that's how I read their comment.
What does this mean?