Most likely its training data included countless Space Invaders in various programming languages.
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i have this feeling with LLM's generated react frontend, they all look the same
Models don't emit something they don't know. They remix and rewrite what they know. There's no invention, just recall...
Trivially, humans don't emit something they don't know either. You don't spontaneously figure out Javascript from first principles, you put together your existing knowledge into new shapes.
Nontrivially, LLMs can absolutely produce code for entirely new requirements. I've seen them do it many times. Will it be put together from smaller fragments? Yes, this is called "experience" or if the fragments are small enough, "understanding".
Humans can explore what they don’t know. AIs can’t.
Based on my experience with present day AIs, I personally wouldn't be surprised at all that if you showed Gemini 2.5 Pro a video of an insect colony and asked it "Take a look at the way they organize and see if that gives you inspiration for an optimization algorithm", it will spit something interesting out.