Before discussing the formless attainments, it says that he had mastered sīla, viriya, sati, samādhi, paññā. This is the same set of dhammas that was later called the indriyas or balas, where, as in every significant doctrinal context, samādhi is defined as the four jhanas. This of course agrees with the many passages that show that the formless attainments always build on the four jhanas as the “successive abidings” or “successive cessations” and so on. None of these meditation states just pop out of nowhere: they depend on conditions.
This is why narrative context and intertextuality is important. Such details are almost always left out of retellings, or their significance is overlooked.
The meaning of these terms is established because they make sense within a narrative context. His experience under the former teachers follows a familiar path, which echoes the later Buddhist gradual training. Going forth, learning the Dhamma, undertaking precepts, mastering the foundations of meditation, gaining samadhi, then on to the formless attainments.
The similarities between the path here and in the Buddhist context are striking and clearly intentional. It is, indeed, because of the similarities that the differences become meaningful.
The problem with the former teachers’ approach was not that there was something wrong with the meditation, it was that it only leads to rebirth in the formless realms. If it wasn’t “real” formless meditation, this is obviously impossible.
What is the purpose of this story? What is it trying to tell us? There is nothing in the narrative to indicate that its purpose is to show that technical terms like “samadhi” or “formless attainments” were used in a different way than their established technical sense elsewhere.
Rather, the purpose of the passage is to illustrate the role of right view, not right samadhi. That’s why the learning of the texts is emphasized at the beginning, and why the bodhisatta rejected “that teaching (dhamma)” at the end. The “noble quest” wasn’t a search for a cool meditation state, it was the search for the end of the cycle of rebirth. The whole narrative is framed around the doctrinal meaning and significance of the meditations, not the meditations themselves.