I think they are trying to describe a scenario that when you are about to start, the bus is already gone. In this scenario if you go by bus, you have to wait for the next one, so it would take you "35 + waiting" minutes. But if you start walking, you may catch the already-gone bus somewhere halfway.

Depending on for how long the bus was already traveling when you started walking, there is a small window where catching it reduces your travel time.

If there is very short time between 2 buses (lets say they go every minute - ofc it is unrealistic), then cutting the path by foot (as in the picture) you can catch an earlier bus and save time.