You know, that’s an hour of the day when most people are asleep. So even if someone is walking to the prayer, or driving to the prayer, nobody sees them.
But Allah says that is the time that is witnessed. Usually, things that are witnessed are the middle of the day. Popular times, popular places, but the masjid is not a popular place at Fajr time, not for most of us. This salah is not a popular time, for most of us. It’s not a time when you see a lot of people around you, but Allah says there is no doubt about it, it is witnessed.
The question is then witnessed by who? Not by other people that are sleeping, not by the people of heedlessness, but rather by the angels that are recording our deeds. Rather by Allah Himself, who’s making note of these slaves that are coming and leaving their sleep for Him and His word.