Slots are rigged at the mainframe level. That’s why the big jackpots at the Indian casinos are always a ‘machine malfunction’. But it would seem to be harder to have your associate get on the right machine at the right time for the payoff if you were trying to deliver a jackpot from the central computer. Easier to rig them to not pay off a jackpot at all.
They put up a disclaimer at the end claiming they didn't know nothing about the provenance of the machine.