It's very difficult for me to describe exactly how I come up with the notions that go into creating one of these 75 or 300 word stories. The best I can say is that the theme or the image suggests something to me, and I see where that takes me.
I can tell you that this particular image suggested all kinds of things to me. I considered (and rejected) such ideas as a human colony on another world, many generations after the landing, having vague myths about their origins in the sky; and about prehistoric humans visited by beings from another world, and the way in which they imagine journeying to the stars. (As you can see, the starscape was the most evocative part of the image for me.)
I then thought about the water and the rocks in the image, which suggested beings who lived in both environments. This led to telling the story from the point of view of one of these creatures. My primary goal was to stay true to that character's feelings and sensations, was making her someone for whom a reader could feel empathy.
(Whether these are aliens who had been visited by humans, or the sentient descendents of modern Earth animals, after humanity is gone, and who were visited by aliens, or possibly by returning humans, is left as an exercise for the reader. It's often a good idea to leave just a bit of mystery in a story for a reader to ponder. Fiction should be neither transparent nor opaque, but translucent.)
(But if you must know, I was leaning to the first possibility. I like HareBrain's suggestion that these are otters better than my own idea.)