Here's the GOES IR imagery from that time. If you zoom into the area, you'll see low clouds. The second image (about 30 minutes after the OP report) does have a faint oval shaped cloud shape (especially to the east of the site), but that could just be coincidence. From my experience, this is either biologicals or a transient atmospheric reflectivity event, either of which would be interpreted by the software as the concentric ring returns.