Yeah, like he said.
The quote refers implicitly to sophomores who have competed at the NCAAs. This reduces the sample to those sophomores who have developed to the point that they have qualified for NCs. Every individual has a limit to their individual potential. Obviously, the earlier that you approach that limit, the more gradual your future improvements will be thereafter. The people in that sample are specifically those that closer to their personal limit.
As the Brojos point out in their chart, this follows through for the other AAs in their sample. Hill, Lowe and Estrada improved from freshman to soph years, but were what they were thereafter.
The “dreams become reality” supporters do not need to despair. It is not that type of runner addressed in the quote. If I come out of HS as a 4:30 miler who ran 30 miles a week, I have more relative “room for improvement” than Chris Derrick. He worked very hard in high school and achieved an outstanding level of success. He placed well at NCs as a freshman and consistently performed well thereafter. From a mile high view, however, he started as a top 10 type runner and finished as a top 10 top runner.
The 4:30 miler, on the other hand, just starts working hard freshman year. They may start to be competitive at a conference level as a soph, may qualify for NCs as a junior and may place higher at NCs as a senior. Most likely, they will not contend for a title, but they certainly have improved. Some, like Shorter, may contend. Most won't