That is, at best, a superficial assessment
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the comparison of RPGs in general and jazz is entirely reasonable. Both G1 and G3, for example, offer considerable opportunities for improvisation, exploring one method of exploration until it plays out, jettisoning it, and exploring another.
By the same token, playing cricket is like jazz, because there is scope for improvisation and the bowler has to choose, from ball to ball, what sort of delivery to use to try and take the wicket.
Or even crossing the road is like jazz, because there's scope for improvisation around j-walking vs waiting for the lights to change, waiting on the median strip or weaving around the oncoming traffic, etc.
All the comparison is really showing is that both RPGing and jazz involve decisions. But then, to the best of my knowledge, so does playing computer games.
If the claim is that RPGing involves creative or artistic decisions, somewhat like those involved in being an improvisational musician, then I think that depends very much on which RPG you're playing. G2 is not really about creativity in an artisitc sense at all (and for that reason is often regarded as the weakest of the G-modules, although it happens to be my personal favourite). It requires tactical or "military" creativity, but then so - I assume - can computer gaming. Wargaming and boardgaming certainly does.
I GMed a session of Burning Wheel on the weekend. In the course of the session the players had to come up with multiple goals and motivations for their PCs (as part of the PC-building process) and had to participate in generating campaign backstory, including history and NPC names and personalities (as part of the action-resolution process for knowledge skills and streetwise-type skills).
As far as artistic creation is concerned, this was more demanding than any classic D&D module (which do not require PC goals or motivation, but rely solely on the XP system to generate player buy-in to the scenario, and which put backstory creation, such as it is, firmly in the hands of the GM). But I stil wouldn't compare it to playing jazz. There is none of the discipline (of rhythm, tone, etc) that is involved in playing, even improvising, music. A better comparison might be to sitting around a campfire or a dinner table playfully composing a light-hearted chain story.