OpenAI's ChatGPT and Sam Altman are in massive trouble. OpenAI is getting sued in the US for illegally using content from the internet to train their LLM or large language models
It is absolutely not theft. If you’d like a physical crime to compare it to, forgery would be what you are looking for. But piracy is not at all theft.
That is, unless you are talking about Captain Davy Jones and his pirate ship. That type of piracy is theft.