Is a wire coiled around a post adequate for grounding light fixture bases?
The wire from above in the left picture is most likely coming from the Romex that powers the fixture, maybe attached by wire nut to ground at the end of the Romex.

This fixture looks fairly modern but I can't see the wiring behind it so unless you pull it down some and look (fairly easy) this is not enough info to be sure.

To answer your question, no, coiling around the post is not adequate grounding.