Yes, that's Ventus talking and it's not the only time it happens.I was wondering where to even put this, but I suppose this is as good a place as any, since it's a disagreement with something I'd read on the forum in the past. I'm referring to a lot of discussion when KH3 was first released about how Sora saved Aqua instead of a character more personally connected to Aqua, and also how it made Riku & Mickey's task irrelevant.
Anyway, I started a re-play of 3 the other day, and the first scene in the Mysterious Tower made me disagree with the above now. Riku talks about how the best way to reach Aqua would be through a friend of hers, comparing it to the way he jumped down into darkness after Sora unconsciously in 3D, because a friend would automatically be able to locate her through their hearts' shared bond. This cues them to say how Ventus and Terra disappeared before she did and Yensid to note that Eraqus could've if he wasn't dead. Then out of nowhere Sora says "I'll save her!" Donald gets angry, Goofy says he doesn't have the power (which Yensid had just got done telling them before Riku and Mickey entered), and then Sora says he didn't understand why he said this. I don't know if there's a Nomura interview somewhere else that discounts this, but I took that moment as Ventus speaking through Sora? Similar to the way Roxas speaks through him in Twilight Town.
I haven't got to the part in which Sora jumps into the realm of darkness to fight Aqua again yet, so my memory's a bit fuzzy on those particulars. My take right now is that Ventus' heart is the reason Sora is able to locate Aqua and appear there so quickly, in exactly the way Riku talks about in that scene; so it isn't really random that Sora saves her, because Ventus' connection with her is how she is saved more than anything else? And then Ventus physically saves her at the Land of Departure once he has his body back. This is probably really dumb and random, but it's just a thought I had during that scene. And it seems Riku's purpose for being in the realm of darkness narratively was Repliku more than Aqua.
The latest catchphrase is "May your heart be your guiding key" which has a literal meaning: during KH3, Sora's heart is leading him to the places he needs to visit and that happens when he saves Aqua too (but it's Ventus' heart). Sora being the one to save Aqua was already set up in Blank Points and then in 0.2's opening. Watch 0.2's ending again:
"May our hearts be our guiding key... You'll know where I am". It's exactly what happens later in KH3 when Ventus's heart leads Sora to Aqua.