A quick search via Google doesn't bring up the answer, although maybe it's buried in there somewhere. It's an interesting question and makes one wonder how all the punctuation marks came into being, and when. Someone must know! How about Lynn Truss? (I never read her book).
Logically the term seems unnecessary. What is wrong with the plain 'stop'? A stop is a stop, isn't it? A thing has either stopped or it has not stopped. There is no part stop.
Perhaps, even before telegrams, there were stops and full stops, and no such thing as a commas. Then when the comma was invented, presumably to replace the stop, it would have been logical, to my mind, to replace the term 'full stop' with 'stop'.
I shall watch this topic with interest.