I get the exact same thi8ng with Select Subject on my computer with your image. So the Adobe Select Subject Ai just thinks that area is part of the subject for whatever reason. There is nothing I can do about it because I can’t change how Select Subject works. You will have to just brush off those area for the affected images.
The good thing is that this is very uncommon. I’ve not see that before. There must just be something the AI has in it’s ;earning model that is picking gup that specific configuration of “shapes”. The AI is trained by Adobe for shape recognition and AI literally has a mind of it’s own.
This is a good example of why the Select Subject tool for selection sucks for automation. It is also why I made the Auto Clear features changes I made to Version 7. It should never erase part of the subject because of the spacing it does. So any failures will be in areas that still need erased manually.
So basically, it is what it is.