Correct. It is a measurement of CPU Time for the process # passed in the first parameter. If the first parameter is blank, then it is for the current process. It is not a measurement of the entire machine CPU time, from the M programmers guide:
"Returns job or process information of the specified process. The format for the $ZGETJPI function is:"
The privilege issue discussed is if you are trying to retrieve information about process other than the current process - you might not have privileges to get that information for another process.