The program itself is almost certainly copyrightable, but what about its output?

These mazes feel like a similar idea to me - he even mentioned that this particular one is generated by a "fibonacci spiral", so there is likely a compact mathematical description of its vertices, and a PRNG (further thought experiment: what if the "randomness" was generated by a true RNG?) along with its seed that was used to determine where the lines appeared. It's an artistic work, but the majority of the "work" was done by an algorithm - he didn't manually draw all the lines.