They guys above have it right. By shutting down the top and bottom vents you had a raging fire that was starving for oxygen. When you opened the Egg you gave it a huge rush of oxygen, hence the fireball. Sorry about the arm hair! I lost an eyebrow in my first Egg flash!
From now on, whenever you are cooking on the Egg get in the habit of opening the lid an inch or so and pause to let the air in slowly. Then you can open it the rest of the way. I just do it every time regardless of temp so I don't forget when i really need to do it.