My understanding is they legally can't. It was trained used OpenAI, which doesn't allow using their output to train new models. Someone would need to find another data source to fine tune llama.
Person A uses GPT3 to generate training data, and publish it on his blog, without representing it as human generated. Person A does not give permission for it to be used by Alpaca team.
Alpaca team comes along, scrape his blog, and uses it as training data, without permission from person A. Now this is fair use, so there is nothing person A can do to stop it, just like how Github scraped our code for Copilot without permission.