It seems to me that he wins the race during the loooong under water portions of the race (seems like almost half the pool length), when he comes off the turns; during the actual stroking he is not pulling away.
Also nice to see a bit of a glide during his stroke.
Because of the long underwater portions he takes by far the fewest strokes of any of the swimmers in the pool. If my counting is correct:
Lane 1: 9-10 strokes (hard to count, many angle changes)
Lane 2: 10 strokes
Lane 3: 12 strokes
Lane 4: 15-16 strokes