Just received this update - ADMINISTRATOR rights need to be used when doing update. First time for everything.
If I had to guess a reason, Garmin Express is installed in C:\Program Files (or the x86 version of the same) and wants to read/write a configuration file or database file that is in the same location. Normal users do not have permissions to write there, so elevation would be required. I also see my my installation, a folder named "Express Elevated Installer." That folder may have had the same name prior to this most recent update.