The article says they exposed people to the shocks and other stimuli to get a response to the 5$ question. It doesn't say they took the people and gave them 15 minutes to play around with the thing. Curiosity is still very much in the game, especially when there's nothing else to do.

A much more meaningful way to do this experiment would've been to have people sit and receive regular shocks (not under their own control), and to sit with nothing else to do, provide an incentive for staying 15 minutes and see how quickly they give up.

And while i'm writing: The article also mentions they couldn't find people who enjoy the time alone, but didn't mention whether they asked people who habitually medidate.

The fundamental problem is that the study is substituting the author's interpretations of behaviors for a simple description of the behaviors. The authors tell the participants to think when they are in the empty room but there is no verification that thinking is the condition the participants avoid by pressing the button and equally, there's no proof that "pain" is the condition they sought by pressing the button.