After downloading the Install packages for the latest update and selecting "Install Later", then later selecting "Install", the status screen still states that it is "Downloading Packages."
The message is misleading as no packages are actually downloaded at that time. The scanner is running initialization of the setup process and is incorrectly reporting what is happening. This has been fixed in SMG 10.5.2 and should not be seen going forward. Until you are able to update it can be safely ignored.