It's poorly worded but they seem to hypothesise that poorer students were sort of piggy backing off of those who paid for the cheats. So they were cheating too.
More interestingly, the teachers (which were the invigilators) rationalized this as "everybody is cheating, if you don't than the stupid kids from the country side would have bigger grades than you, so you should cheat too" (I was in an elite school).
The bribe was not huge (around $50 total sum per class per exam), so I don't think it wasn't the primary motivator for the teachers. Way more money was made by private untaxed tutoring.
So I wonder a bit at what makes education ineffective. I coached at risk latino high school students briefly while attending college and for them it was pretty clear that they needed to work to help support the family so they had fewer hours to devote to study. I suggested to the program that paying these kids minimum wage to spend time with a tutor would pay for itself in reduced social services costs and police costs down the road but they were not interested in hearing about that.
*edit: and yeah, when it comes to the exam, you're no longer educating. literally the only important thing for both student and teacher at this point is the score