Great leaps of improvement from freshman to sophomore year is very routine especially when that runner is new to the sport. All it takes is SOME training versus NO training to make a big difference.
There is also a simple change in outlook that can account for big jumps early on in training. In most areas of your life you start from the simple and progress toward the complex. A freshman will participate with no context or goals but as they return as sophmores they are often motivated to exceed what they did last year, to run faster than a rival, follow the footsteps of an upperclassman or hit a qualifying time for a big race or championship.
When everything is new it's easy to get faster. There is no formula except to run regularly. Most of the Footlocker finalists do the same training for the most part. There are no secret workouts just slight variances in volume or intensity.
If you want to get better just run more.