I really think this reflects what liability Hubitat wants to take on with the Implication that use may put on them if it was stated to be an alarm system.
What is an alarm systemi in it's simplest form when you think about it. It is a set of sensors that protect your property and notify you when something happens. When you dig a bit deaper though security systems are also hardened and validated to ensure reliability. They also include some kind of seconday communication to ensure reliable notification. That is something that Hubitat technically can't really do and provide the flexiability it does.
I think this is really about liability and setting proper expectations and ensuring proper risk assessment is done.