Very interesting that attachment by Mi Yuting (who smiled as he played it) inside the 6-4 stone (about 22 minutes in). It rather goes against normal how-to-approach-corner principles and plays into hane at head of 2 bad shape, but because the 6-4 is so much further away from the corner than normal you actually get quite a sizeable corner territory in exchange for the big influence you give:

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I also recall a game Lee Sedol played against a high stone, maybe a 5-5, in which he played a similar attachment inside to get a big corner in exchange for a big wall. Go is such a vast game .

I am pretty sure the game you refer to has Lee Sedol also playing the 5-4 attachment to a 6-4 stone played by Gan Siyang.