What is the difference between pmset and systemsetup sleep options?
In this case, systemsetup is a high level wrapper that is analogous to the System Preferences UI. Both call the lower level power API which are the internals about how the system actually stores these values for the hardware to use and implement. pmset is a lower level tool that reads the API/hardware values directly, so I would generally trust that over the higher level tools like Energy Saver or system setup

If you are right and there is a discrepancy, you might have to file a bug report with Apple to figure out if it's really a bug or just that the information is being mixed up before it is presented to you.

You can go directly to the source file as it's stored at /Library/Preferences/SystemConfiguration/com.apple.PowerManagement.plist and perhaps it can break the tie between which of these three tools is telling you the correct information?

In all my computers, the numbers match up, so perhaps the systemsleep values are incorrect for your hardware or OS build?