A slewfoot in itself could result in a game misconduct and suspension. Now add the extra push when the opponent is already falling. Let me guess, you're one of those "normal hockey play" guys? Watch Matheson's stick between Pettersson's legs. He didn't manhandle him, he cheap shotted him.
A stick between the legs isn't a slewfoot. A slewfoot is when a player uses their leg, to make contact with the back of an opponents leg, usually the knee area, to make the leg buckle and the player to fall. A slewfoot can cause injury. A stick between a players legs as the player is body checking them isn't a slewfoot. It's more of a can opener. He went in for the hit, the stick went between the legs, he hit him against the boards cleanly, and then threw him to the ground, which arguably could be a roughing minor, or maybe you can call a tripping minor for the can opener, but that didn't affect anything.
There will be 0 discipline, let alone 10 games lol
It's unfortunate EP got hurt, but there's nothing suspendable there. Would I bet upset if Marner got hurt in a similar way? Yeah, but loads of fans would be telling Leaf fans to shut up and it was fine if it was Marner instead of EP.