An external network drive is being counted in the Macintosh HD drive - what's up?


After getting starting disk full errors, I loaded OmniDiskSweeper to help find large files and eliminate or move off of the main hard drive. I was able to successfully remove or move about a third of the HD. Then very quickly it was full again. I ran OmniDiskSweeper and found that my external Apple Time Capsule (not running as Time Machine) was showing up as a volume on my Macintosh HD. My other externals don’t show there. It appears to be counting the external drive as part of the capacity of the 1TB Macintosh total and thus quickly filling in the space I created earlier. How do I get the tree of the Macintosh HD to not include the network external drive?