Prof. Loh is referring here to the area of the green wedge, which is shaped like a big pizza slice. The "V" angle of the slice is of measure 120 degrees, which is one-third of the circle (a circle has 360 degrees in total).
Imagine you were cutting a huge apple pie into three gigantic slices; each person would get one-third of the whole piece, and each person's piece would be approximately the same shape as the green wedge above.
Happy Learning,
The Daily Challenge Team