Nisan was referring to an assumption: IGNORANCE>FALSE BELIEF, for all beliefs. You are referring to the related assumption: If TRUE, then BEST TO BELIEVE, so TRUE BELIEF>IGNORANCE and TRUE BELIEF>FALSE BELIEF, once again, all of these for all beliefs.

I don't think either are widely assumed around here, and I think the link JGWeissman provided shows that.

the assumptions common among brain scientists. Those assumptions that are born from an inability to grasp beyond the dimensions of the space of their current understanding.

Like many others, I'm not familiar enough with the field to have any idea what those assumptions might be.