The context is literally that parenthesis are token weight multipliers, so he's multiplying the importance of "disfigured feet" to the negative prompt by 1.1 th

The context is literally that parenthesis are token weight multipliers, so he's multiplying the importance of "disfigured feet" to the negative prompt by 1.1 three times. There are even other tokens in there that he multiples with less than three layers of parenthesis