A scenario is called independent if the outcome of one event will not influence the outcome of the other. We are trying to assign a position for each player so that everyone gets a position. But we also need to make no one can have more than one position.
Let's say we have position X, Y, Z for player A, B, C. First you assign the position for player A, there will be 3 possible positions (A/B/C). If you assign position X to player A, player B can't get the X position so the possible outcome is only two(B or C). This makes the scenario dependent because the outcome of the first roll will influence the possible outcome of the next roll.
