Its a fun story, but I am told, just not true. The origin of the term "to lobby" comes from England and parliament and refers to the lobbies where the members of parliament would assemble before going into the chambers to debate and vote. The process of researching this word reminds me that the Internet is NOT a substitute for solid reference material, probably in print, next to your computer terminal.
The implication is that the term "lobbyist" is not uniquely American in the least, it is a shared term of art with our brothers in crime, Great Britain.
The Willard Intercontinental Washington