Nervous systems are roughly 550 million years old, and life has been improvising them ever since — into shapes almost nothing like ours. An octopus keeps most of its neurons in its arms, so each arm half-thinks for itself. A jellyfish has no brain and no centre at all — just a net of nerves ringing its body. A nematode worm runs an entire life on exactly 302 neurons, every connection mapped.
No two of these are the same — and no two within a kind are, either. Every nervous system is a one-off, tuned by body and history and the particular world it grew up sensing.
So read neurodiversity at face value and it can't mean only us. It means the whole living spread of ways to have a nervous system. There is no standard nervous system, any more than there is a standard mind.