The term 'safe' varies a lot based on context. In this context it is being used to mean 'memory safe' - i.e. that the compiler can eliminate a class of behaviou

The term 'safe' varies a lot based on context. In this context it is being used to mean 'memory safe' - i.e. that the compiler can eliminate a class of behaviour that are the root of a number of recent security issues. "Safe" in the context of medical and aerospace means something very different, but is much closer to the meaning of "Secure" in this context. No compiler is ever going to prevent you writing insecure code - there can always be a logic problem, bad choice of crypto algorithm etc..