To me the city looks circular with land north of it. If you look closely at the video (or this screen https://serebii.net/blackwhite/sunday3.jpg ) you can see a map. It's round and has pier type things coming off of it. Above the city looks green, so possibly land. I've got a feeling the dark green dot is the current location of the player too.
I'd say you're right. Sure seems to make sense. Definitely seems to be a pier like area and the dot makes sense as it's situated right around the area you would be (east exit/entrance.) Makes me wonder what exactly those white dots represent? Maybe places you can take a boat somewhere?