In this section, Thomas was bragging about how he can dunk to his friends at Lunch. Until Mathis said he can't even clear a 6'6 in jumping
So Thomas proved him Mathis wrong by clearing the 6'6 with ease. Thus proving Mathis wrong in the clearing.
Mathis begins to explain that Thomas is really gifted. The coach doesn't believe Mathis at all.
While Thomas was clearing 7'0 or 7'2 with ease, Holmes had a issue completing them. Holmes couldn't go higher like Thomas.
Thomas ended up winning the competition, but it stopped there for him as far as competing wise.
Thomas then finds out the truth about why he's so good at jumping. He learns that he's gifted with a giant Achilles tendon. That and he's height make him gifted at jumping. While Holmes had a normal sized Achilles, Thomas had a giant one.