Um, this is highly region dependent. If it were a hot day, I would be comfortable interviewing with a CEO in nice shorts and a clean t-shirt, and fully expect that they'd dress similarly.
The example wasn't just "an interview" it was "a high end restaurant" but TBF the outcome is indeed highly dependent on both region and the personal preference of the CEO.
I'm not sure I'd be interested in interviewing with a CEO who can't be bothered to dress up. Hot weather is not a reason not too with AC and fabrics specifically for hot weather.