Probably it was running in the background. If active, garmin software will try to 'grab' a device if it detects one being connected. So you needed to only change that in GE's Settings (Gear symbol) and uncheck the box "Always keep Garmin Express running in the background" to stop it loading silently on PC booting rather than uninstall it completely. Or for a single session right click the GE icon in the system tray and quit it.