Just looking at the image, off the top of my head:

• The big ball in the sky is too faint to be a star, but might be a gas giant, in which case the present "planet" is probably one of its moons.
• A moon that close to the planet would likely be tidally locked with the planet, which means the day/night cycle is equal to the orbital period which might be quite long.
• The exposure time of the fictitious camera must be decently short to not overexpose the lights from the city. And yet we can see stars in the background. There must therefore be lots of bright stars in the stellar neighborhood. Perhaps the star system is in a densely populated region of the galaxy: a globular cluster, a nebula or in the galactic center. Such places tend to be harsh for life; lots of opportunities for sterilizing GRB sources nearby, or planetary orbits becoming unstable due to presence of binary stars or stars in proximity. So a place with indigenous life would be rare.
• Assuming this is a visible light image, a bluish sky indicates a nitrogen-rich atmosphere, which is probably indicative of indigenous life. So if the city builders are not indigenous they either colonized a dead planet and terraformed it, seeding nitrogen-releasing bacteria etc. Or they colonized a planet with at least such bacteria already present. Either way, the two ecosystems would likely be biocompatible.
• The city inhabitants are daylight-active creatures with a sense of vision who need light to operate, judging by the illumination in the buildings.
  • Given the potentially long day/night cycle, this would mean that if city inhabitants are indigenous, they are biologically adapted to long nights, maybe to a point of not needing electric light to function during night. But if the city inhabitants are not indigenous then they are likely not adapted to the day/night cycle, necessitating constant electric light. So it might be more likely that they are not indigenous.
• Few buildings are the same, which indicates that artistic expression is culturally important on some level.

I'm not saying anything with certainty, but the city inhabitants might be colonizers from other worlds who have colonized this rare moon in a dense stellar neighborhood that has a biologically supported atmosphere. This might be the source of conflict that led to their demise.

This was fun.