I think you might have hit on something. It may well be he WASN'T read his rights, and that's why the chief kept saying he's a smart man, he's well aware of his rights.
I don't think the chief ever said "yes, we read him his rights". Rather, he knows his rights.
Hmmmmmmm.
The more I think about this, your point is really key. If he came in as a "witness", and LE kept insisting he was there voluntarily, he didn't have to be read rights. The way you treat a voluntary witness is different from the way you treat someone who is arrested. It's only with an arrest that rights are read, and strictly adhered to.