How does Unity figure out generic component type as Wall in Project: 2D Roguelike tutorial?

Unity released a tutorial for 2d roguelike game a couple days ago: http://unity3d.com/learn/tutorials/projects/2d-roguelike

In the project movement of both enemy and player units are handled by MovingObject script, which first attempts the move by checking collisions. If collisions return true, a generic component is passed, which later is assumed to be either a Wall or Player component to deal damage. Here is the AttemptMove code sample from MovingObjects from the project:

         protected virtual void AttemptMove <T> (int xDir, int yDir)
             where T : Component
         {
             //Hit will store whatever our linecast hits when Move is called.
             RaycastHit2D hit;
             
             //Set canMove to true if Move was successful, false if failed.
             bool canMove = Move (xDir, yDir, out hit);
             
             //Check if nothing was hit by linecast
             if(hit.transform == null)
                 //If nothing was hit, return and don't execute further code.
                 return;
             
             //Get a component reference to the component of type T attached to the object that was hit
             T hitComponent = hit.transform.GetComponent <T> ();
             
             //If canMove is false and hitComponent is not equal to null, meaning MovingObject is blocked and has hit something it can interact with.
             if(!canMove && hitComponent != null)
                 
                 //Call the OnCantMove function and pass it hitComponent as a parameter.
                 OnCantMove (hitComponent);
         }

How does either Wall or Player component picked and not say Transform, SpriteRenderer or any other component?