This is my interpretation.
The tool gives an idea if it could be a real HD recording. Then it must be decided on the basis of conditions whether this is the case.
I expect that there should be enough energy present outside the 16/44.1 spectrum. If all energy is within 22.05 kHz and 96dB then there is a chance that the master was a 16/44.1 and therefore a dubious HD recording.
This still could sound awesome. Nothing wrong with Redbook.
But it is probably not an HiRes recording.
Depending on the instruments, microphones, mic preamp, etc it is possible that on a HiRes recording there is nothing outside the 16/44.1 area