Well, from the pic below, something wasn't hooked up. Have no idea why the wires in the pic are simply taped up, or what they are for. Perhaps some non-installed safety valve?
Regarding the explosion and the danger (or non thereof), all I can say is this: it was very similar to a blown tire---quite frightening. Whether it would have hurt someone or not, I don't know, but I believe the simple discharge of gas may very well have done so. Remember, something (I don't know what) hit me in the left leg just above the ankle as I had my foot on the ground outside of the car on the driver's side while seated. It hurt! So, just imagine what that could have done had someone had their face poking around in there. If you Google "blown AC compressor", you'll see photos of ones that physically blew shrapnel shots out of said compressor (the very first one I see is from an SHO---not good). Also, see the vid below:
https://www.youtube.com/watch?v=J7MfYy2U0Zc