I think that the author is speaking about their world, in which they regularly encounter a specific use of trigonometric functions which would be simplified (conceptually and computationally) by skipping the conversion from and into radians.

> redefine the known world around a favourite detail

I think that's a good way to think about software optimization. Deep inside nested loops of a game engine (TFA's example code comes from Godot), that's often what you need to do to squeeze some performance characteristic into your hardware.