Mathieu Dufour and Eric Le Sage Play the Poulenc Flute and Piano Sonata

Here's some fine playing from Tokyo's Hamarikyu Asahi Hall in 2006: flutist Mathieu Dufour and pianist Eric Le Sage performing the Poulenc Flute and Piano Sonata. I just love the energy and colors they create in the final movement. But how on earth does Dufour manage to play the final high F of the second movement so quietly and effortlessly?