I concur, although judging by the 'speed' of the first a/c I would guess the viewpoint of the camera is well over half-way down the runway, so I would think the 'g/a' theory not likely since reverse is still 'in' on No 1 at that point - and up to 'off-frame'. I think the first may even have been beginning the turn-off at the end of frame, and it certainly did not appear to have any reverse spray at all in the whole visible run.
The concentration on serviceable reversers IS relevant since in all my 737 flying, landings on 'slippery' or 'contaminated' runways are not allowed with one locked out. If you aquaplane, it is only the reversers that will stop you - for a while.
So - was the runway 'slippery when wet'? Was it 'wet'. Was it 'contaminated'?
Obviously the enquiry will hopefully have all these answers but I think it is important to lay this 'reversers don't matter' trend here.