I may technically be using the term sting innacurately, but it generally refers to a particular short melody or short riff, that is used as a kind of specific evocative musical ‘phrase’ in a movie, or a whole soundtrack, or even in a videogame.

Often the simple sting itself can become iconic, and/or be repeated in different variations throughout a larger composition or longer set of scenes.

https://en.wikipedia.org/wiki/Sting_(musical_phrase)

But yes, generally a guitar sting involves more than one string.

… I guess unless its that ramshackle slide guitar Jack White assembled in about a minute, that one time.