It looks to me like the initial explosion was at the upper part of the rocket. Reminded the Starship explosion https://x.com/NASASpaceflight/status/1935548909805601020 where on 0.25 speed also visible what the start of the catastrophe was at the upper part.
Interesting that just 2 days ago NASA picked Blue Origin instead of SpaceX for this year Moon flights.
On a sidenote, one can wonder how much, giving coming SpaceX IPO, it costs for Bezos to hire a Starship engineer :)
Analysis video by Scott Manley notes that other comparable tests did not have visible fire at all, so it seems it started lower on the rocket and that the upper fire ball was either a secondary explosion or something coming up the transporter stand: https://www.youtube.com/watch?v=aaR6yEE-Myo