If dictionary definitions had legal force in this context I suppose you could argue that playing music is "a personal action", and therefore 1a applies, so premeditation is not implied for it be to counted as "spontaneous"; singing a song on the other hand is an utterance, and 1c would apply.

Am I right in taking it that there is in fact no definition of what is meant by "spontaneous" in this guidance document? I imagine that in the absence of such a definition a court would probably not use a dictionary, but would dredge through ancient law books to find precedents. Or, since the word "spontaneous" does not appear in the Act, it would probably treat this highly ambiguous section of the guidance as essentially meaningless.