When applied in an integer decrementing variable (otherwise no reason for -- unary operator), !--x is false until x === 0 because of the falsy nature of 0.
You are 100% right when you are saying it's just a way to confuse the next person maintaining the system, its just a hipster way of asking
x === 0 ?. So:
!2 = false; !1 = false; !0 = true.
Hope it helps.