That is a bit of an uncharitable reading. The subchapter literally preceding the example you cited is titled "Existence & Uniqueness" and explains why those concepts are important to mathematicians, and right following the stated theorem the author explains it in minute detail and gives an informal phrasing ("there is a unique degree n poly- nomial passing through a choice of n + 1 points"). The entire chapter is devoted to how to take these kind of complex looking statements and understand what concepts are behind them, and the author explains the concepts in both normal language and how one would normally see them in a maths textbook.

You are right that this book requires high school level math knowledge, as it's the equivalent of a first (and maybe second) year math course. Most programmers I have met do display that amount of knowledge however. What other starting point (or topic) would you suggest for teaching someone mathematics that can be related to programming?