I think it is fairly easy to see how his running form differs from that of the others. Bikila demonstrates how movement is naturally initiated by spinal action – that the head and spine lead in vertebrate locomotion and the limbs amplify the action of spinal muscles. I wrote about this here:
One can see the difference in Bikila’s form from that of his companions – the dominance of his trunk in his movement is evident. His arms and legs are not retracted as are those of the other runners. Note his arms, nicely hanging from the lead of his head. His legs are not retracted, allowing him to let his forefoot contact the ground, rather than his heel, which would be the case if his leg were retracted and his toes lifting on leg recovery.
The other runners all show evidence of the presence of protective, retractive reflexes, which tend to inhibit natural spinal movement and increase the effort required to move the arms and legs. I wrote about this briefly here:
The Alexander Technique is a method to guide students out of retractive, protective patterns so that healthy postural reflexes can function without interference.
I wrote about the Alexander Technique and running here: