This is a perfect example of the old saying, "the whole is more than the sum of its parts."
The number of people who are asking how this is possible, need to think about how these things interact, not just how many seconds they are worth (individually):
1. amazing pacing through 1200m of a 1500m (they had a guy who could pace for 4/5ths of the race),
2. in a neck-and-neck competition all the way to the line,
2. after living and training at altitude,
3. with the best teammates to motivate him and push him in practice,
4. along with the best coach in America (of this generation) who is not afraid to train him hard but also (patiently) gave him a year to develop,
5. and access to the super shoes which are truly amazing (if you haven't run in them, they are miraculous).
6. But most importantly he is a one in ten million human talent.
So, assuming he was a typical NCAA star of the 1990s, he would have been running 3:40. Do the 6 things I listed above add up to 7 seconds? Not on their own (because we had good teammates in the 90s and we had good pacing). The difference is that the interaction of the better shoes, better tracks, higher expectations and create and upward spiral of fitness and psychological readiness...