The GIF movie on
https://www.inverse.com/article/20788-spacex-falcon-9-explosion-ufo-anomaly suggests explosive combustion starts (or at least most easily exits the skin of the rocket, but that's never armour-plate strength) just below the payload shroud, which is where I'd expect the orbit-raising final stage motor to be.
(The UFO is, IMO, a bird at mid-distance. Neither large and fast and far off, nor fly-sized and fly-speed and near, but a normal sized and normal speed bird at some point significantly between camera and pad, clearly flapping. It is mere coincidence that it is in frame, and doesn't even
look like it hits the craft. Even if it was a drone, it can't be directly responsible by colliding, giving it clearly does not, and doesn't get caught in the explosion.)
Apollo 13: stirrer (necessary for destratification in zero-G?) with inadvertently arcing wires, IIRC.
Challenger: Booster seal made brittle by cold, causing catastrophic failure in use.
Neither seem to apply to this pre-test refuelling incident. But note that SpaceX is on record as having pinpointed the cause as being a LOX tank's internal helium bottle strut failing, in an early ISS delivery attempt that failed. This by the use of internal sensors capturing audio of the event (given very little first-hand examination of the resulting debris being even possible), so to have so early on started to say that this accident is a complete puzzle, needing video to perhaps answer at all, suggests that even if they
have internal data, they're looking at something external to their own equipment and entirely unaffected. Or they're being very cautious about a pressure-skin failure, for business reasons (their own, or a supplier) not wanting to get caught up in a defamation or incompetence lawsuit situation before they have enough evidence to make it a legal certainty, whoever ends up being in the wrong.