Design Patterns - Abstract Factory - EnchantedMazeFactory

I have a question regarding the Abstract Factory pattern sample code from the Design Patterns book.

The book presents a simplified and partial example of a maze game where there are walls and doors connecting rooms.

There is a basic MazeFactory class which has the following factory methods:

class MazeFactory {
public:
    MazeFactory();

    virtual Maze* MakeMaze() const { return new Maze; }
    virtual Wall* MakeWall() const { return new Wall; }
    virtual Room* MakeRoom(int n) const { return new Room(n); }
    virtual Door* MakeDoor(Room* r1, Room* r2) const {
        return new Door(r1, r2);
    }
}

The author(s) then define a specialisation of MazeFactory:

class BombedMazeFactory : public MazeFactory {
    BombedMazeFactory();

    virtual Room* MakeWall() const { return new BombedWall; }
    virtual Door* MakeRoom(int n) const { return new RoomWithABomb(n); }
};

I don't know exactly how RoomWithABomb should work but lets say it creates a room which has a 5% chance of containing a bomb and if you open a door which contains a bombed room you explode.

Now lets say the client creates their maze using the BombedMazeFactory class and they create some rooms. The rooms created are of type RoomWithABomb*, however the factory returns a Room*.

In order to implement some maze game logic I would assume you would need to check whether a room contains a bomb, but Room* has no knowledge about bombs. The only way we can find out if a room contains a bomb is to cast Room* to RoomWithABomb* which is bad practice right?

Is their example not very well thought out or is there some other way of handling cases such as this?