R/W 20 would not have been too short for this take-off. The same result given the same circumstances would have happened if R/W 25 had been used. This is because take-off calculations give the crew the lowest power setting that will achieve V1 at the point where there is just enough runway ahead to stop again. So the difference on r/w 20 compared to 25 is that on 20 the power setting would have been more, but the stopping distance on either runway would have been the same.
High speed abort never a nice situation having had one myself in a 747-200.
My guess is a weight shift after V1 (perhaps on rotation), thus making the a/c unflyable (so taking away the choice of trying to still get airbourne), but sadly not enough runway length ahead to still stop.
CL
Looks to me like crew did a fine job