My daughter was messing around with one of my buggies and accidentally had the negative bullet in the positive terminal of the battery and then she touched the positive bullet to the negative terminal on the battery but didn’t push it in. She said when she touched it, heard a pop of sorts and took it apart

I’ve checked it all out and the battery checks out fine and the ESC seems fine and looks to have all functions. What/how should I check it out further? Do I need to check the external cap?