Imagine a train track with detectors every 2 miles that will detect the presence of a train. Also imagine that we have a transponder placed near the middle of the train that triggers the detectors when it passes.
If a very short express train less than a quarter mile in length has passed mile 6 but has not yet reached mile 8, the best that the system can tell anyone is that the train is somewhere between mile 6 and mile 8.
Now consider that we have a very long, heavy freight train that is three miles long. At times our three mile long train will be next to two detectors, with the transponder in between. At other times, when the transponder is within one-half mile of a detector, the train will only be next to one detector. When the transponder is between detectors, we still won't know exactly where the head end of the train is.
Basically, the sensors in the lens that report distance information to the camera are like the detectors every two miles along our train track. They tell the camera what positions the lens is focused between. The "Focus Distance Lower" is the closest position the lens might currently be focused at. The "Focus Distance Upper" is the furthest position the lens might currently be focused. The lens might actually be focussed anywhere within that range.
Why in one of the pictures (shallow DoF) is the difference between focus distances higher than the DoF, and in the other picture (deep DoF) is the difference between focus distances lower than the DoF?
The depth of field is like the length of our train. With a wide aperture, we have a short express train. With a narrow aperture, we have a long freight train. We only can sense when the focus distance in the middle of the DoF crosses from one detection zone to the next, just as we only have a transponder in the middle of our train. With a deeper DoF the edges of the DoF may or may not be past the "Upper" and "Lower" focus distance, but we can't know that since only the position of the actual focus distance can be measured as anywhere between two of the detectors at various positions between minimum focus distance and infinity.
The camera only reports the range of the actual focus distance, the focal length, and the aperture used. EXIF Info makes an educated guess at the DoF based on combining those three factors.
In the end, DoF calculations are only estimates. Since depth of field will change for different display sizes of the exact same image, any camera estimate of DoF is only a guess based upon an assumption of the intended display size. The long standing assumed "standard" is an 8x10 image viewed at a distance of 12 inches by a person with 20/20 vision. But in the digital age that goes out the window very quickly when pixel-peeping.