Yes, this is true. There is no way to scan software installations for another user than the currently logged on one (except we perform a broader search through the registry which we currently don't do for performance reasons).
You might consider setting up logon scripts on the computers in your network which initiate an
LsPush scan after every user logon. If history logging is enabled, you can find per-user installations in the history of your assets (or in a report including tables
tblSoftwareHist and
tblSoftwareUni).