800 is a very technical race. It requires an optimal balance between aerobic and anaerobic running. Guys like Rudisha had very good aerobics, but weaker anaerobic running. So he was at his best running from the front and creating a huge gap. If it was big enough, he cruised to victory.
Nijel and this Wanyonyi have a weaker aerobic but strong anaerobic composition (what we call finishing kick). If they stay close to the front, they can more or less sprint the last stretch. Their style is almost like galloping towards the end, using gravity to gain momentum(the similarity).
Narrow hips are okay - actually advantageous - for running in general.