When Windows Update scans on its own, the results of the scan are put in a cache. That is the list of updates you see in the WU queue. It is static (the cache does not change) until Windows Update again scans on its own.
Each time you use wushowhide or the “usoclient.exe StartScan” command, the list of updates is current (dynamic). That manual scan that you do does not change the Windows Update cache that is generated by Windows Update scanning, so what you see in the queue does not change (or reflect the current available updates).
When you hide updates with wushowhide, that does not change the cache=WU queue. But what is in the queue is what will be downloaded and installed. So, in order for the queue to reflect the removal of the updates you hide, Windows Update has to be forced to rescan on its own to clear the queue=cache of those hidden updates so they don’t download/install.