I have not seen precisely this identity before, but it seems to be a variation on Chapman's identity [R. Chapman, Amer. Math. Monthly 109(7) (2002), 664–666], see also arXiv:math/0612464,
$\sum_{x_1,x_2,\ldots x_N=0}^{1}(-1)^{x_1+x_2+\cdots x_N} \;\text{det}\;(x_1 A_1+x_2 A_2 +\cdots x_N A_N)=0,$
valid for any set $A_1,A_2,\ldots A_N$ of $d\times d$ matrices, with $N\geq d$d+1$.

