I remember something about this particular syntax, but I cannot find it in any of my documentation. If I had to guess, I would say since == is a binary operator, and it is evaluated left to right that the first two values are compared, and because the result is “not equal” (or false), then the following compare would be False == n, which, since N is 0000 is true and thus the end result is a “pass” on the constraint.
If you know where this example is in some documentation, then a reference would be appreciated.