None; are the thrust reversers not moved by the pneumatics on the 767? The hydraulics don't have much to do with it on the GE powered -300s. I'd suggest they may have had both reversers?
A very nasty situation. Landing high and probably heavy means you're carrying a lot of energy. Add into the mix a Flap20 landing that the pilots almost certainly have never before done for real and some reduced control authority. The jet is almost certain to float unless driven positively onto the runway. It's not hard to see how what was observed could have arisen.
Assuming that the pilots were, like me, just plain vanilla line shags, I suggest that they did ok. Perhaps shutting down on the runway would improve the outcome next time. Easy to say from the comfort of an armchair.