You’ll have probably noticed by now that the Sun doesn’t set in the video, but instead goes round and round. This is because when the video was shot, the ISS was orbiting parallel with the Earth’s terminator line. The terminator (not Schwarzenegger, this time), or twilight zone, is the moving line that separates day from night on an object illuminated by a star.
The location of the terminator changes depending on the season. When the ISS lines up with the terminator it dodges the shadow from the Earth and consequently the crew onboard the satellite get an unfathomable view of the Sun.
The ISS orbit only aligns with the terminator a couple of times per year, around one of the solstices, so this footage is pretty unique.