Whenever I order diet coke on tap, I always double check when they have taken my order that they understood 'diet' and then when I get it I check with them again . I can taste the difference probably but don't want to take any chances. It seriously matters as I won't obviously have bolused for a pint of normal coke which probably contains about 25-30g carbs.
That said, diet coke doesn't ever affect my BG levels. So I can drink away without impact.
Mixed grill chicken often has honey or something sweet on it to make it char nicely so be careful for those carbs too.
Have a good meal!