You had a double charge...it's that simple.
The other explanations would be: Poor metallurgy? Not likely. Squib? Not for that kind of blow up. God's will? Nah.
I used to own a Dillon RL450...wonderful press. I also owned a Square Deal B...specific for pistol calibers and I had ALL the conversion sets! Dillon makes top notch stuff no doubt. But it wasn't Dillon that failed...it was you.
You failed because you trusted the machine to get it right every time. You stated you've loaded over 5,000 rounds...statistically speaking your gun blew up at just the right point for an overcharge to have occurred due to a mechanical malfunction. (Yeah I know the machine CAN'T malfunction, so this only means that somehow you malfunctioned.
The rise of progressive reloading machines at prices "anyone" can afford has carried with it a rise in KA-BOOMS...
This is one reason I REVERTED to the old, slow, time-consuming process of true HAND loading. Sure it takes time to powder 50 case "batches" but then I can visually SEE they are powdered! It takes longer to prime 50 case batches but I KNOW the primers are well seated. It takes longer to work each case through a manual press but at EVERY STAGE of the process my hands are on that round and my EYES are on that round.
Progressive presses CANNOT be "perfect." Commercial grade, fully automated loading machines sooner or later produce a squib that reaches the consumer. Why do you THINK factory ammo is loaded WEEEAAAKKKK? Because they're biasing their loads so that the INEVITABLE overcharge doesn't result in a blown gun....
The ONLY way to "roll your own" is to go each step in turn...physically handling each case and component, and actually SEEING what is going on. Anyone who needs to churn out a thousand rounds a "session" would be better served paying the vig for FACTORY ammo and accepting that at those consumption numbers statistical probability is STILL going to catch up with them but when it does the factory has already mitigated the outcome such that one generally does not end up with a blown gun.
I'm sorry to see a beautiful gun blown up.
It's good that you were not injured.
But it's time we stop pretending the cause could be anything OTHER than what it statistically MUST BE....and start trying to get people who choose to load their own ammo to approach the matter as conservatively as possible.