Your claim that it's arbitrary doesn't really have much weight without further reasoning.
The priors referenced in the “technical details” doc (and good lord, why does everything about this require me to dereference three or four layers of pointers to get to basic answers to methodological questions?) appear to be based entirely on proxies like:
> Responses such as moving away, escaping, and avoidance, that seem to account for noxious stimuli intensity and direction.
This is a proxy that applies to slime molds and Roombas, yet I notice that neither of those made the table. Why not?
I suspect that the answer is that at least when it comes to having zero neurons, the correlation suddenly becomes pretty obviously reliable after all.