> But what about when we're told 'This coffee is not hot'? Does that mean we think it's cold?

I think it depends on your training and how you've studied to interpret statements with logical operators such as these.

If I interpret "not" as "anything but", and if the possibility space of "anything" includes more than one state (temperature, in the article's example), then "not hot" should be taken to mean "any temperature but hot".