Is it possible the crew retracted them in an effort to increase weight on wheels after touchdown. Not that I am condoning such a practice but it seems strange for them to be retracted. What Vapp would that aircraft need in that configuration. I know in the MD-11 you would dang near a dry lake bed to stop it clean if you were heavy.
That's the whole purpose of the speed brakes, destroy the lift over the wings upon touchdown, putting all the weight onto the mains for max braking effect.
Why would they run the after landing checklist and not stow the reversers? Not only that, but once that thing broke in two, I doubt they had any control over the flaps or motors, which leads me to suspect they landed that way, and that was the position the thing came to rest in!