This happens all the time. It's almost never plagiarism.
People who don't create regularly can sometimes fall into the trap of thinking all their ideas are unique and beautiful. Once you've been writing, drawing, painting or whatever for a while you come to realize that none of your ideas are that original and what counts is how you execute the actual art piece.
There are tons of paintings of the night sky but Van Gogh still created a unique and beautiful piece of art from it because of his skill and technique.
If you look around long enough you can always find another piece like yours. Especially when you're focusing on a very specific subject.




