That sutta describes what the Buddha did in a particular situation.
He did that to get his message across to various audiences that included aristocrats, brahmins … householders … ascetics … the gods under the Four Great Kings … the gods under the Thirty-Three … Māras … Brahmās.
– The first several categories were all human.
The point of that particular sutta was the following: The Buddha wanted to get his point across to those who were there at each of those assemblies without letting them know who delivered that message. Among those human assemblies, he appeared as a normal human, not as Buddha. Among deva assemblies, he appeared as a common deva, etc.
– I am not sure why the Buddha did not want to reveal his identity in those cases.
That does not mean others (including devas or brahmas) can do that or even need to do that. Some may be able to do that.
– Once a deva came to the Buddha ask a question. But with his fine body, he could not stand straight and was wobbling, just like a tall, cylindrical helium-filled balloon would sway back and forth.
– So, the Buddha asked that deva to “manifest in a human body”. Apparently that deva could do that and created a “human-like solid body” for himself. Then he was able to stand firm.
But of course, the Buddha would not appear in a brahma realm with his actual physical body. One normally visits those higher realms with the manomaya kaya (gandhabba kaya). Even then, those devas or brahmas normally know who it is (unless the Buddha willfully concealed his identity, like in the above case).
– It is probably not possible to appear in deva and brhama realms with one’s physical body. Those realms are located well-above the Earth’s atmosphere and there is no oxygen to support a physical body.