I suspect he stopped the roll in a panicked attempt to pull the other way, far too late.
Unlikely to be g-loc, nowhere near enough G nor for nowhere near long enough imo. He might have done better to have pulled up more.
I reckon someone forgot that when starting a barrel roll from wings level half the height of the roll will be above the starting level and half below it.
An aileron roll or even a properly executed slow roll is hazardous enough at that insane level, but stands vastly more of chance of working than a barrel roll. In any case those manoeuvres should never have been attempted without a significant up-line being established before commencing as islandlad pointed out above.