What exactly do you mean by proactive/reactive here? In my (admittedly limited) experience, Exalted games tend to be very proactive in that they allow players great freedom in determining the means of solving any given problem they face, but fundamentally reactive in that these problems (and often, the player's goals) are set before them by the ST. I don't think I've ever been in a game that did not start by positing a crisis and asking the players how they react to it.
Often times, games are
started by these kinds of inciting incidents, yes. They're the one scripted sequence that ideally lets the players settle into their characters and get used to the game. The difference is, Exalted wants you to do that
sparingly, and instead, after doing something, let the players direct the game.
Like, this comes back to the 'tutorial' of Exalted that is implicit but very poorly communicated inthe books, that you are intended to let players grab huge fistsfuls of the world, shake, and see what comes out. Scripted, on-rail plots are traditional concepts that DnD and similar games hew to by their nature, before they pushed further and further into 'combat engines' and not 'roleplaying games'. (This is not a bad thing, exactly)
So in theory, (which is harder to apply in practice), Exalted is supposed to work like this: You present your players with a situation- usually something tailored to their backstories and motivations. Like- "You all are in Nexus for similar reasons, and the situation has conspired that you all meet and greet."
Or , more artfully, you have already worked together and the introductory session is the Big Confrontation, no messy footwork yet. (Exalted likes to skip that stuff, remember?).
Anyway, so you resolve the inciting incident, and then in a standard Solar game, players are then asked "So now what do you want to do?"
If the game and ST have done their jobs well, they'll be buzzing with ideas and feeling power at their fingertips: "I want to take over Nexus!" And then the ST starts figuring out 'okay, what do you have to do to take over Nexus.'and communicates that to the players-. The players are the ones who think of METHODS (charm, kill, buy, etc), but the ST decides the terms of success.
So when we say 'proactive', we mean players set an actionable goal in the game world and then take actions to accomplish it. These can be Conquest, Fame, Material Wealth, Vengeance, whatever.