I'm pretty sure that was just edited footage.Remember when Gamefreak revealed Crabrawler at the Pokémon World Championships and showed it KOing Mega Kanghaskhan, Landorus-T and Talonflame to hype it up as some new super competitive attacker?
...How the tables have turned.
Also, the Kangaskhan wasn't Mega, it was just a regular Kangaskhan.