So how did he get caught? It doesn't make sense to bust somebody on a college campus for downloading 30 songs when there is probably some kid in the dorm next to him with thousands of downloaded songs.
They only busted him for 30 but there may have been many more. Also targeting a low level user sends a message to other low level users that it’s not just the 10,000 song sharers getting busted. My guess they feel they lose more from very many people sharing relatively few songs than from a few people sharing lots of songs. And it follows the concept of “broken window policing” (i.e. fix things when they’re small and they never get big.
I seriously doubt they selected those to target randomly. They likely had 10s of thousands to choose from and went after a cross-section of those sharing music so as to send a message to others in each targeted demographic. Probably also tried to avoid certain demographics like single working mothers or they’d face the publics wrath.