The best idea for this situation is generating an event when actor or some component hits on the collision box component;
Casting from Other Actor to your specific class is just programming idiom casting happens on runtime base-derived class inheritance checking.
Also there is another ways to communication with blueprints like [Event Dispathcers][2], [Blueprint Interfaces][3] and making as a public and setting that variable after put actor into the game world.
And most tricky one is using of Get All Actors of Class node returns arrays of references regarding to specified class. This method is not effective for large countable objects in the game world. This call iterates all of game objects in the world may cause that performance issues.