It doesn't. All things are executed locally. All keys are random and all private keys are known. If you want to attack real keys, you have to change that code, because it is only an example, where all private keys are first generated, and then limited to some range. Then, this generator only can show you that the attack works in practice: for locally generated keys, it can find a solution.

If you want to attack for example 120-bit key, then you have to modify that code. For example I tried using 120-bit "z/r" and 120-bit "r/s". Then, from 120-bit puzzle key, I've got 240-bit nonces. If you add N-bit number with N-bit number, the result has N+1 bits. If you multiply N-bit number by M-bit number, you can get M+N bits. By combining those two rules, your nonces could have: "(bit(119)+bit(119))*bit(120)=bit(120)*bit(120)=bit(240)". Then, after checking 100 random signatures that are guaranteed to have no more than 240 bits, you can see that it doesn't work. It is not random enough. It would work if you could use some 120-bit key, add some 256-bit value, multiply it by another 256-bit value, and somehow reach 240-bit value. But as it is not the case, the randomness in "z/r" and "r/s" is not sufficient to recover any key in that way, because both added and multiplied values are not random enough.