The Leafs AHL affiliate, the Marlies, have offically been eliminated from the playoffs which is why multiple players have been brought up to the NHL.
It is a typical move for an NHL team to call up all their AHL players that are under contract once the affiliate team is eliminated, in case of injuries.
This isn't anything. It's common for teams to call up their entire roster of NHL contracted players when the minor-league team is done.
One of the players who has been called up is former Leafs tough guy Kyle Clifford who is the Marlies' captain. Even though he has been called up, it is very unlikely he dresses for any games.