Photo light question: How was this halo effect created?

My dad shot this photo on a recent trip to Canada. What's striking about this is the halo effect around the lighthouse, which was not added in post-production. (Despite my many attempts to convince him otherwise, my dad doesn't shoot in RAW or use Lightroom or similar tools for photo editing, so this is all natural.) He and I are both very curious why this is happening. His theory is that the water vapor behind the lighthouse is catching the sunlight, which is diffused outward. Does anyone know for sure what's going on here?Shot on a Nikon D7200 at 1/2000, f/5.3, ISO 400 with a +⅓ overexposure. via /r/photography https://ift.tt/2vDx3kb