[bludvein]

I was referring to this though.

Sun Wukong later single-handedly defeated the Army of Heaven's 100,000 celestial warriors - each fight an equivalent of a cosmic embodiment, including all 28 constellations, four heavenly kings, and Nezha, the son of Li Jiang Jun who proved himself worthy - and proved himself equal to the best of Heaven's generals, Erlang Shen. Eventually, through the teamwork of Taoist and Buddhist forces, including the efforts from some of the greatest deities, Sun Wukong was captured. After several failed attempts at execution, Sun Wukong was locked into Lao Tzu's eight-way trigram Crucible to be distilled into an elixir, (so that Lao Tzu could regain his "pills of longevity"), by the most sacred and the most severe samadhi fires. After 49 days, however, when the cauldron was opened, Sun Wukong jumped out, stronger than ever before. He now had the ability to recognize evil in any form through his huǒyǎn-jīnjīng (火眼金睛) (lit. "fiery-eyes golden-gaze"), an eye condition that also gave him a weakness to smoke, and proceeded to destroy Heaven's remaining forces.

The flashback was probably from his rebellion, when he didn't have the eye condition yet. He seems to have lost it in addition to his amnesia. Though maybe they just aren't using that part of the myth?