I am going to remove the "obvious reason", I will also cite at least two article that indicate that the area positively has a molasses smell in the summer. Your reasoning sounds logical but that does not take into account the fact the people’s basements were filled with the goo, On houses that where not destroyed you could see the high ‘molasses’ point which would mean that wooden timbers, brick walls and field stone foundations were permeated. As a local Bostonian I can also attest to the smell which can almost be nauseating at times. Maybe it is just the molasses covered ghosts but it is there.