The Buddha explained in the sutta quote below that he attained the knowledge of the four noble truths and became completely liberated, all in one night.
On the other hand, a stream enterer is one who learned from a Buddha and has completely understood the four noble truths through insight, but still has seven more fetters to overcome before becoming fully liberated.
As such, we can conclude that the Buddha did not go through the four stages to become liberated. Rather, he attained it all in one go.
A Buddha attains the knowledge of the four noble truths only after fully overcoming ignorance. A stream enterer learned the knowledge of the four noble truths from a Buddha, then overcomes ignorance later.
"When the mind was thus concentrated, purified, bright, unblemished,
rid of defilement, pliant, malleable, steady, & attained to
imperturbability, I directed it to the knowledge of the ending of the
mental fermentations. I discerned, as it had come to be, that 'This is
stress... This is the origination of stress... This is the cessation
of stress... This is the way leading to the cessation of stress...
These are fermentations... This is the origination of fermentations...
This is the cessation of fermentations... This is the way leading to
the cessation of fermentations.' My heart, thus knowing, thus seeing,
was released from the fermentation of sensuality, released from the
fermentation of becoming, released from the fermentation of ignorance.
With release, there was the knowledge, 'Released.' I discerned that
'Birth is ended, the holy life fulfilled, the task done. There is
nothing further for this world.'
"This was the third knowledge I attained in the third watch of the
night. Ignorance was destroyed; knowledge arose; darkness was
destroyed; light arose — as happens in one who is heedful, ardent, &
Here's an analogy.
The Buddha is like Einstein who discovered the Theory of Relativity. He's the only one, and there's no one else like him.
The stream enterer is the physics bachelor's degree graduate who studied relativity and passed. He has proven understanding of the breadth of physics, but not the depth. He has entered the physics academic stream.
The once returner is the physics master's degree graduate. He needs to return to university one more time to do his doctorate.
The never returner is the physics doctorate graduate. He doesn't have to return to university again to do a degree, but he still needs to build up his research portfolio and experience.
The Arahant is the tenured physics professor. He has reached the peak of his career.
Einstein obviously never studied relativity for his degrees because he is the one who discovered it and instantly became the first professor of it.