[pfflier]

Sounds plausible. LOX coming in contact with any kind of hydrocarbon can do this. The catalyst can be an ignition source or even pressure.

The event appeared to be external of the booster, like you speculated, near the base ring or the flame bucket. Regardless, that booster is definitely going back to the shop for some rear end repairs.

[Celtic Conservative]

And the ground team is going home for fresh underwear.

CC