When I first saw this I was wondering why Winnipeg High School Football League was playing rugby with a football. So what happened? The Winnipeg (Manitoba) Kelvin High squad got in punt formation and received a solid punt, that is when things get weird. The punt returner punted the ball BACK down the field (yes, it is legal) and it sent everyone after the ball and the receiving turn was lucky enough to get there first and run it a couple yards into the end zone.

Prep Rally explains why this is legal in Canadian Football:

Unlike American football, Canadian football holds that once a punt travels more than 10 yards downfield, the kicking team can recover the free ball and regain possession. In this way, Canadian punts are essentially just like American kickoffs.
However, in a nod to rugby, Canadian football holds that on scrimmage kicks (i.e., punts and missed field goals), the returning team can respond by immediately punting the ball back to the other team, creating a free-for-all where whichever team gets to the ball first will retain possession.

via Prep Rally