In step 24, you're lifting the white layer shown in 25 while Elias-stretching the second triangular flap (just a spread-sink, essentially). Then in 25 you're folding the bottom corner behind while swinging the top bundle of points back dowh to its original position.
The mountain crease in 24 is correct--it just is missing an arrow in the central region that would say to lift that portion of the model.