It could be any one of the three theories, but I would choose either one or two, maybe even both. The only way it wasn't them is if they survived on air or something in the atmosphere, or if they did not need anything to survive, which I highly doubt since I have already surveyed most of the world.
This world consists of two supercontinents, and on each, there are only three of those ponds. Though they are very deep, they are also very far apart. So far, in fact, that they could be said to be at the edges of the continents they are on. Although I have found their residents, they truly are among the only few living beings on this world. By scanning their internal body structure, it is evident that they must survive on this liquid or they have developed a unique mechanism for survival. That was my conclusion.
My AI's conclusion was that both options one and two were potential choices. It didn't believe they possessed a unique survival mechanism, based on scanning their soul strength. However, it should be noted that soul strength can never be accurately measured; it will always be an estimation. There have been rare instances when weak soul strength gave birth to TAMA.
They continued their journey and engaged in a mundane conversation about their people back home. How could I understand them? I am a HUMAS; we can read minds, but we surpassed that limit millennia ago. We can discern your words from your very intent as you speak, and our AI makes it even easier by simply translating everything you say using the same method. However, theirs was more advanced as they utilized your soul's intent, and the soul can never deceive. Their speed was impressive; they were at least at the 'Ari-king stage.' After a few more days of stopping at similar caves to rest at night, they finally reached their home. I am a little excited to see it again.