Just my opinion but I don't believe that we should be in the "punishment" business with scouts, that is for the Judicial system. Use the incident as a lesson in the importance of telling the truth ( I am sure the scouts got a lecture that day anyways) and then let it go.
On a lighter note, it is tough for boys to resist spitting off of anything that is high or crosses anything, kid won't spit all day long, cross a small foot bridge and "spit", why I don't know, it's in the male DNA I think. Putting boys up in a lighthouse and them getting in trouble for spitting seems to be "entrapmen