Computers generally and software as well, are completely incapable of "lying".
It is not always a good idea to believe everything you see on a screen, because the software shows what it is programmed to show, and that does not necessarily reflect reality.
In order to "lie" you have to know the truth. Machines don't know anything at all.
Summing up various things often results in considerable discrepancies. This can be due to many things. Various units, like GBytes, incorrect interpretation or display of those units, etc etc.
If you want very accurate analysis of various things, then you need accurate tools and the wherewithal to use them.