The LLM started with a three month headstart, both in terms of code, using the previous game as a template, and more importantly, all of the learnings and mistakes you made in the hand-coded pass.
Not only that but it was also their first game, meaning they faced a ton of unknown unknowns which are no longer there. If they were starting to program a card game today without LLMs they would still be able to apply all the knowledge and insights they gained from the previous experience; it would take significantly less than three months.