From the Huffington Post, an explanation:
So why are prisoners in the Philippines such excellent dancers? Because dancing is part of their rehabilitation. In July 2007, Filipino inmates performing "Thriller" became a viral sensation garnering over 10,000,000 hits on YouTube. The performance included 1,500 prisoners, who practiced up to four hours a day.
The man who uploaded the video below, Byron Garcia, is a security consultant who was hired to reform the Cebu prison after a series of riots in 2004. Amongst other initiatives he started an exercise regime that turned into dance classes. According to the "New York Times" the "inmates' health has improved and recidivism rates are down dramatically."