New Lens Blur tool in Lightroom

I have used this tool in some edited pictures and found it very useful. I am inquisitive to know what happens when I take a picture with a very wide/large aperture and use my focus point to an area away from the subject —in a completely different spot in the picture. Is the software designed to automatically look for the subject and choose it by default or does it "see" where the original focus point was on the camera and then picture and then start from there? This is probably a question for Adobe engineers rather than the community. It may also factor in where I am setting my focus point on.