What it means to be a “systems” programming language is a matter of some debate, but there is at least one definition that’s only coherent in a resource management model isomorphic to RAII/ARC.
For example, while resource acquisition and release may be deterministic, there is no implication that a released resource may be immediately reused or reacquired. This is not pattern most software engineers are used to. The reason for this is that hardware may hold a lingering reference to a software resource even if the software does not -- and hardware doesn't use reference counters or destructors. An arbitrary amount of time may pass between a resource being released in software and that same resource being available for reuse again in software. Many people new to systems engineering make the mistake of reusing a resource that was released but not reusable.
Systems programming languages don't just ensure deterministic release of resources, they also need to provide a way to express that the hardware may hold references to objects the software has fully released such that it isn't really released. This is not something the average programmer has to deal with, but this is part of what makes systems engineering different.