i'd imagine that if they used prosumer cameras for some action shooting, many are limited to 60fps at only 1280x720 resolution, which is probably the mode used if they wanted to achieve clean slomo footage at 24fps, without using "twixtor" type software slomo interpolation which can look quite dodgy. Having said that, some of their slow motion footage looks like it was on a more expensive overcrankable camera maybe capable of +120 fps as it is quite slow and clean
If they had to stabilize the footage digitally after it was shot, and if the footage was quite shaky, they might have lost much of the image around the edge of the video frame, and then had to crop it down to close to DVD resolution as a result.
Therefore even though it was shot in a form of HiDef, they only had a smallish dvd size resolution to work with in the end.
this is just from my experience and only a guess at what they did