Is something up? Probably not. If he was awake, my guess is that the light in Msgr. Gänswein's office (the window to the left of the Pope's study window) would be on as well. When the Pope is awake, nobody sleeps in the Casa Pontificia. My guess is that he went to bed and somebody left the light on.
But it makes you think: With the Synod going on, would the Holy Father "pull an all-nighter" to study?