"Carlisle Tire's warranty used to state "tires must be inflated to sidewall stated pressure or warranty is void"; I don't know about now though.
How in the world do they determine if the tires are inflated to sidewall pressure? Is there a little gremlin with a report card in each tire. Some manufactures just never get out of the box.
Unless it was a bad tire, had been run flat previously, and most likely a bunch of other possibilities. At the time of a blow out there is no way they would know other than by assumption.
Yes, most probably operator error, but only assumptions."
Sorry, but there are ways to identify the probable inflation & load history of a tire. Just as a Medical Examiner can do an autopsy and identify the signs of bad diet and poor or no exercise, or years of smoking, it is many times possible to see the physical signs of low inflation and high load.
These signs can show up in the indentation into the tire left by the wheel.
Here are examples of improper inflation or a Run Low Flex Failure of a P type, ST or LT type tire.
Melted body cord is physical proof of extreme run low
Also, the different flex markings can be seen on the interior of a tire. In extreme cases the Innerliner (special rubber that holds air in much like a tube did in tube-type tires)
Manufacturing "Defects" will usually result in early life failure i.e. <1,000 miles. Tire failure is in itself not proof of some nebulous "defect" even though lawyers and those not experienced in failed tire inspection want to think so.
Once you examine, in detail, a few thousand tires from both controlled testing and from day to day use & abuse the conditions seen in tires tell a story of the tire's history.
Too often people simply think of the conditions (load, speed, inflation, road) at the moment the tire fails as the "facts" to be considered when trying to decide the "why" a tire failed. In reality, the damage might have been done hours, days or even months earlier.
See THIS post on a study of pot hole damage and how long it took for some tires to fail from the impact.
As I point out in my "RV Tire Knowledge" Seminars at RV Conventions, tires are like potato salad, putting the salad back in the refrigerator after it was left for hours in the hot sun does not "fix it" and make it good to eat the next day any more than taking the burnt hot dog off the grill and letting it cool down before serving it makes for a good meal. Adding the correct air in a tire after running it low for thousands of miles, does not repair the damage. Slowing down to 50mph after hours of speeds of 70 to 80+ over the preceding weeks and months does not "fix" or heal the thousands of microscopic cracks that were formed in the overheated and overstressed belt rubber. Once a crack is initiated it does nothing but grow. If a person stopped his smoking addiction of 2 packs a day for 40 years a couple months ago, will his lungs be clean and clear today? Not a chance.
When examining a tire, I look at the physical condition of a tire and specifically what evidence there might be. Years of experience has taught me what to look for and allows me, as a court-certified "Expert", to form an opinion that is based on the examination of many thousand tires.