I'm pretty sure that was an intentional joke. I do wish it'd have been a bitwise AND with 1.

Clearly the solution is to factor each number and to (recursively) test the parity of the sum of the factors. Since all prime numbers other than 2 are known to be odd, the parity test for the case of a single factor is easy. You only need to special-case 4 to avoid an infinite recursion.

Author should have perhaps bootstrapped a script that doesn't use modulo?