I figured it out and it is because I wasn't paying close enough attention.
I was listed as the Owner, because I Owned a sub-group.
That was my first mistake.
Then I didn't type in "I understand" when I (attempted) to delete the sub-group.
I then tried to quit the group again and still got the message that I am the sole owner
It was at this point I asked the question.
I then went back and tried again and again until I figured it out.
I needed to read the delete group pop-up box completely and type in "I understand", deleting the sub-group.
I was then able to leave the group.
I had to wait until the question was approved to tell how my my sad story ended.