Instant fifth dragon? Help!

I was over at my friends house and he was playing Gragas jungle. A team fight was about to happen at drag. A enemy started by using his Ult on dragon. Mid animation ult stopped it and a ate while his ult hit. Not sure if that's relevant or not. Regardless following this jumped over the wall dragon and getting an instant 5th dragon buff for both teams. Following this event every dragon taken by either side was considered a global fifth dragon buff that included receiving 354k gold.

http://tinyurl.com/pvppeg9 It was fun but pretty sure this isn't suppose to happen.