Canada: Punt Returner Punts Ball, Team Recovers for a Touchdown

Is this legal? According to the YouTube comments, yes.

Yes it is legal. There were five players behind the punter (on the returning team) when we punted it back, and therefore they were “onside.”

According to Prep Rally once the football travels 10 yards on a punt, it is a free ball, the same as a kickoff.

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.

Canada! Am I right?