Slew-footing is the act of a player using his leg or foot to knock or kick an opponent's feet from under him, or pushes an opponent's upper body backward with an arm or elbow, and at the same time with a forward motion of his leg, knocks or kicks the opponent's feet from under him, causing him to fall violently to the ice.
Armia was issued a 2-minute penalty on the play, which is definitely the right call.