Could be the artefacts in the image. But in that case they normally give you this as a reason. The second reason could be that they don`t see a market for this image (art).
OK, I could follow if they decide to say that there would be no market. This might be understandable.
But the reason was clearly technical reasons, which is linked to wight balance or colour settings.
it makes no sense for me for this kind of pictures.
A: Low commercial value. The "background" is odd, and the subject is unlear.
2: You didn't submit it with your watermark in the lower left, did you?
1. OK, if you are right, they can tell it to me. And they accepted the pure background. No commercial value is OK and understandable, but not with the reason for rejection as technical issues.
2. No, of course not. I used the smartphone for the post. I just have the internet version on it , and they are watermarked.