By design.

The study isn't saying that social media usage causes increased sensitivity, it's saying that they are correlated. It makes sense that people who are more sensitive to social recognition would be more drawn to social media usage.

They think pixels on a screen are their friends.

You could've just wrote todays kids are pussies and summed it up nicely

It could be an indicator of obsessive compulsive disorder, or a precursor to addictive behavior. More study is needed than one isolated association.