They don't know that. It's the hypocracy of not using their service to infringe on someone elses copyright. The only way Compaq could legally have a PC BIOS is by having one team reverse engineer the original and describe what it does and another team reimplement it.
Yes, it's completely hypocritical because of how LLMs are built. That doesn't change the fact that if you're offering a service online, you'd try to prevent abuse in order not to be held liable.
You can do the same with LLM. Have one session document something, and other session write up an implementation, with nothing but docs shared in between.