Interesting. I can think of a few scenarios that might be at play here. I assume that the increase is just a slight statistically relevant bump. It could be that more copies of MP heavy games sell after people pirate and enjoy the SP campaign. I.e. the demo effect. Or it could be a general statistical trend where piracy increases the amount of gaming occurring and that pirates either induce sales in others or eventually cave in and start buying games when they are gainfully employed adults.