Some things that help telling real world from game: in both the weather is quite uncertain, so in the real world, correctly, road surface is sharp in the foreground, while more distant objects are slightly hazy and the sky's blue is washed out, in the game road surface is blurred even in the foreground, while cars are very sharp, buildings have less details than real ones despite being less hazy in the distance and the sky's blue is bright. Also, in one real photo, there are sun reflexes.
Anyhow the sky's brightness alone wouldn't be discriminant, as in real world we'd have it washed out if it didn't rain yet, but very bright if it just rained very strong and the clouds were remnants before good weather returns.
That said, quite impressive pictures.
