I see no compass rose on that map, so let's use left and right. if the complaining owners' property is to the left of the Sacketts', then some portion of the water was diverted. If the complaing owners' property is to the right - and what you say is true - then by filling in their property the Sacketts prevented all of that drainage to the right of them from draining to the 'lobe.' It would hit their property like a dam and . . . flood the adjoining property. Which gets us back to the very beginning. Filling 85% of that property could cause the adjoining property to flood. A lot more than I first thought, if you're right about the lobe.
Drained by the borrow ditch on the side of the road, adjacent to the swamp. Note that the area between the swamp and the road is not labelled "wetlands".
Still, I don't believe we should be arguing these fine points -- it misses the issue. Which is: SHOULD A FEDERAL AGENCY HAVE THIS KIND OF AUTHORITY, TO REGULATE MUD PUDDLES IN A SMALL COMMUNITY IN RURAL IDAHO?
I submit the answer is "No". There is evidently a local board empowered to issue a building permit. They are far more capable of judging the circumstances than is the EPA or any other federal agency.