ATLAS AGENA ROCKET DEPRESSURIZES ON PAD, COLLAPSES AND TEARS ITSELF TO PIECES

The vehicle is designed to hold all that fuel, plus whatever payload it carries on top, but it's not designed to have heavy loads attached to it in any other way. Rockets are so intensely optimized for weight that sometimes they're barely strong enough to stand upright if you fuel them the wrong way: ▶ this video .

Yes, the Centaur upper stage was and still is using balloon tanks. I think this is the failure you're referring to: ▶ this video And here's a picture from ULA/Tony Bruno showing a Centaur tank in their factory, being supported by a rig: link

I think it is implied in the article that only the motor is massive enough to excavate a crater. The similarity in size of the craters suggests they were created by objects of similar mass. At least one early rocket design (Atlas) had fuel tanks so insubstantial that they had to be pressurized until they were loaded with fuel on the pad, and a loss of pressure could be expensive... ▶ this video

For the record, a couple Atlas rockets did crumble under their own weight due to unexpected loss of pressure: ▶ this video And some Atlas missiles on display are still being pressurized to this day: link Like really, there is a compressor next to the rocket that keeps constant pressure inside against the slight leaks. Pretty impressive for 40-50 old rocket left outside exposed to the elements to be still this airtight. :)