Power Spots come from a combination of approved Wayspots and an imported database. It was probably just added in the recent sync of Power Spots from the database if you have never seen it used before. See this explanation:
You can see Power Spots on the nomination map screen as exclamation points with the toggle on. If you tap it and it just has a placeholder image instead of a photo, it was definitely an import. If it has a photo, it is harder to tell, because photos can be added to power spots through edits.