Good grief it’s BOTH superior genetics and superior training. That’s why becoming a world class athlete is so difficult.
What the brothers display is that East Africans are not the only ones with superior genetics and youth training. Many East Africans grow up running to and from school. That is no different training stimulus than what Jakob did as a youth. Obviously he also has a genetic gift to run. However, without the training he would likely be another 4:0? 1600m high school kid. Which is very good but no where near a 3:30 1500m!