Is your question what is the meaning of the "short" tag?
The answer is: That you have a short connection, and the handler should make sure it's transfereed immediately (sort of a priority tag, although I hope it work's )

If your question is, why it's purple?
Well that's too difficult for me to answer, perhaps one of the experts might know (When connecting via Zurich with Swiss, you get a Orange coloured tag, saying "short connection at Zurich")