The cloud was absolutely water bending. Aang used airbending to fly up, but collecting the water means you’re condensing the water vapor that is mixed with air and specifically moving the water into katara’s waterskin.
Also to respond to a couple other comments at the same time:
@nesc@lemmy.cafe Yes, waterbenders can bend steam, and change it’s phase. In The Drill, Sokka breaks a pipe, filling the room with steam, to get an engineer with schematics to come. When he shows up, Katara flash freezes him in place, using the steam the had filled up that room.
As for air controlling any gaseous substance, I don’t think we have any idea if other gasses could be controlled by an airbender, but since “air” is a mix of a bunch of different gasses to begin with it stands to reason they could bend a number of different gaseous substances. And for waterbenders, probably just depends how much water is in that liquid. We know blood and perfume can be bent by waterbenders, at the very least.
@Majorllama@lemmy.world Lavabenders belonging to earth bending makes perfect sense, as lava is literally molten rock. You yourself said “water can do ice and stuff since that’s just a phase change”, and that’s exactly what rock into lava is. The ability is pretty rare though, as I imagine it takes a lot more “power” to phase change earth than it does water, as it’s melting point is so much higher. Also, as Toph says, earth is a stubborn element, so it takes a very powerful bender to produce, or more often, an avatar. Metalbending is actually much easier for most earthbenders to learn, as lavabending was used by Kyoshi at least if not discovered earlier, but metalbending became much more widespread even though it was discovered hundreds of years later.
As for what does air get? Spiritual projection mumbo jumbo. Also vacuum creation.
There are other sub bending specialties too. Combustion (fire), sand (earth), healing (water), sound (air). So they all get a buncha extra stuff than just the base “bend your element”.
And now I have gone on waaaay too long about this.
That I can’t really answer, as there’s no real in universe measuring stick for bending power. Some people clearly just have more oomph to their bending though, though I can’t say if any bender could reach that peak level through training, or if they have to be born with a certain level of talent/power. Zuko certainly shows that bending can improve through training. In flashbacks we see him struggle with basic bending techniques, and little natural ability.
Conversly, in that same flashback, Azula makes a good argument for natural talent, being a bit of a prodigy at it. Korra takes that argument even further, being able to bend 3 elements when she’s like 5 or something.
If we think of the time the Gaang assaulted the earth palace to talk to the earth king, we see them fight through pretty much the entire Dai Li/palace guard to get to the king. These would all be highly trained earthbenders, some of the kingdoms elite. But they essentially get chewed through by 3 kids.
So basically, much like real life, training can help a bender improve. A lot. But also like real life, sometimes people have just a ridiculously high natural ability that pushes them above the herd. Aang, Toph, Katara, Azula, these are the Jordans, Gretzkys, Kobes of the bending world. So both nature and nurture.