Thank you to all that have responded to the thread.
Now that everyone has shared their experience, it is my turn to weigh in on the three points in question based on my own experience.

1) Fiction. It is quite common knowledge that a freshly lube-tuned springer that is dieseling violently, to the point of achieving detonation, can be settled by shooting a few heavy pellets through it. Shooting the heavy pellets result in a much milder dieseling, which will slowly burn off any excess lubes in the compression chamber. After several heavy pellets, the mild dieseling ceases, and at that point, shooting the lighter pellets will no longer cause dieseling nor detonation. This practice that has been around for decades seems to directly contradict the theory presented in the first part of the noted statement.

2) Fiction. It is highly unlikley that an experienced airgunsmith would make a statement like that. I would be more inclined to expect some inexperienced wannabe to make such a claim in hopes of gaining some "cred". Yes, some abuses can appear readily apparent from the condition of the spring, but unless the suspected abuse can be verified by the owner of the gun, you are just guessing. For example, I had a Diana 34 in for repair, which had it's mainspring shattered into 6 pieces, with numerous fractures in the coils as well. I suspected dry firing as the cause. In speaking with the owner, I discovered that he had been using plastic, 3 grain pellets in the gun exclusively. IMO, that is about as close to dry firing the gun as you can get. The owner was advised on the best pellet weight to use in his freshly repaired gun going forward.

3) Fiction. I have had some guns in for repair that had some major damage due to detonation, and not one of the owners had experienced having the gun re-cock itself. Bulged compression chambers, front plug (complete with barrel still attached) blown completely out the end of the compression chamber, broken stocks, etc. Just to elaborate, dieseling is when there is a puff of smoke, of varying degrees, emitted upon firing, but if there is sufficient "fuel" and heat generated by the dieseling, then detonation is achieved - producing a very loud bang. It is the energy produced by that contained explosion in the compression chamber that is what causes the damage to the airgun.