What you have linked to is the Quick Start Guide, made in 2015. The manual has far more information that you need to read and know, otherwise you will encounter more problems that aren't mentioned in the QSG and you will be back on the forums asking for help again. The manual was changed to include the other method for shutdown. Both methods are listed, but the left-stick-down method is preferred. Here is the full User Manual v1.8, the latest revision.
Why DJI haven't removed that method from the manual and quickstart guide is unknown. That method does still work but it can have unintended consequences. Perhaps send them an email or contact their support office directly and ask them. This is a public forum and DJI do not always read nor respond to posts here. Sometimes their employees do take part in the discussions, but this is not the way to get changes made.
If you have successfully landed the aircraft but the motors are still running, you will notice they are running quite slowly at an idle. Technically, it is spinning the props with just enough power to sustain that altitude, which isn't a lot because the ground is supporting the weight. If you then do a CSC, it will try to do a weak right turn and move left and back as you move into the CSC position. This is only for a few milliseconds, but it has the result of tipping the body diagonally through one of the rear arms, and depending on the terrain could also result in the prop hitting the ground. This in turn causes the whole aircraft to lean back onto the back arms causing both props to hit the ground before the motors are disarmed. It should not be a particularly violent action at all unless there are other factors e.g. a strong wind pushing it over.
Now, if you have performed a CSC before the aircraft is on the ground fully, the motors will still be spinning quite quickly, supporting the whole weight of the aircraft. The resultant incident will be far more energetic, and classed as a crash. Maybe you were a little too quick to perform the CSC as it was your first flight? Perhaps wait a bit longer until it is on the ground fully, and the motors slow to idle before stopping them.
There is no way a CSC tilt-over will destroy the aircraft as you make out. A CSC from any altitude in-flight can cause a crash, even if performed only inches above the ground. There is even a warning in the manual not to do a CSC in flight or it will fall out of the sky and crash. If you did manage to flip the aircraft as you say, you must have done a CSC in the air. But then you would have other problems which you did not describe. If it flipped over on its back, it will not respond to shutdown commands from the remote and you will need to manually turn off the battery or disconnect it. You would have complained of this, or smoking/burning motors or ESC.
So if you have killed or destroyed your drone, it is likely pilot error. If you just clipped the props on shutdown, you would have followed DJI's instructions as published and would have a case to lodge a complaint with them. But it would not have killed anything.
Perhaps if you include the extent of the damage, we could tell if your description is exaggerated or not and advise you of what is involved in fixing it. You may not be aware but these aircraft contain a flight data recorder which is also transmitted to your controller and recorded on your device. You can upload them and share them here so we can see EXACTLY what happened and what you did, and advise you further. That record is sent to DJI by the Go App and they get to see exactly what happened as well, should you try to make a warranty claim etc. It is pointless making things up or exaggerating because the facts in the flight log are all that matter.
You aren't the first person to have had this happen to you and I've read many on the forums complaining of the same thing. None have had their aircraft destroyed or burst into flames. I personally have shut my motors down using this very technique. Every time was a minor tilt or lean over. A few times my props clipped the landing surface (a carpet offcut, so no damage to my props from gravel etc.), plus I regularly fly with prop guards in place. In time the procedure was revised and I have never performed a CSC on the ground since. So I think I am experienced enough to offer you advice. You are probably going to get more help on the forums by not snapping at people trying to assist you.
You also mention you have "(phantom 3 professional, updated)", which I read to mean it has been updated to firmware 1.10.90. This firmware increased the shutdown time from about a quarter of a second to 3 seconds. If you are flying on this firmware, and tried a CSC on the ground this may have created a more violent situation for a longer period. As the aircraft has no concept of "being on the ground", it thinks it is always flying until the motors are shut down. Having the aircraft lean over after landing, but waiting 3 seconds for the motors to disarm would be an eternity, and during that time the motors would be spinning up from idle quite severely, as distinct from previous firmware. This possibly could cause the props to strike the ground ferociously, and possibly damage the aircraft body, or cause it to tumble over. Yours would be the first post I have read of this happening to someone if this is the case. Most people on 1.10.90 would be experienced enough to use the left-stick-down method.