I'd make the same assumtion I think a lot of people do that's why I've been moving threads around from there. I'm gonna try and make the description a bit better for what should go in there because it's not clear and as I normally search forums myself when I'm stuck I know it's easier to find answers if they're where you expect them to be.
I'd say you're doing pretty well for a newbie
that image looks really nice to me so far I like the water. I've never used the node you're working with which is why I can't help but I render a lot in mr so I might be able to figure out where to find some info on it. You can get some strange results especially with final gather and banding artifacts when you have your quality settings too low a lot of the time so adjusting these in your render settings is always worth a try but it might be something in the node itself that needs adjusting. Something tells me as this is fog it's more likely the case. It does look similar to a problem I had a while back though which was fixed when color corrected and increased quality I seem to remember, so take a look at your render settings.