I asked about a dress code for Bistro when I ate in Chiefs D'France in Aug. I was told there isn't any dress code. I said I was asking about the restaurant upstairs for a future visit and I was specificially told the restaurant is in a theme park and there isn't any dress code.
I was wearing a polo style shirt with dockers so I guess I would have meet the old dress code. I asked my waitress so I'm not 100% sure the information is correct but I suspect Bistro is a lot more casual than it was a few years ago.