Streaming in the viewer isn't like streaming a video. It just downloads individual images "on demand" and stores them in memory (never to disk). To use streaming, you have to query a CC ImageServer (PACS) and open a study directly from it (via the DICOM Explorer).

If you open individual files from a mapped network drive (via My Computer) that's not streaming, that's just opening a file from a network drive.

Have a look at the Workstation User's Guide and maybe you'll get a better idea (top of the page under Resources/Documentation).