Not an expert, but I would imagine the speed at which these carbohydrates get metabolized is a factor in whether or not it messes them up? Carbs from bread take a much longer time to raise blood glucose levels and do so for longer than a spike induced by drinking what is essentially liquid sugar.

Drinking sugary liquid like coke causes very rapid rise in blood glucose levels and will require excessive amounts of injected insulin to maintain glucose in reasonable limits (which may lead to dangerous drop later).

Eating something with high carbs is much slower and can be managed with normal insulin doses. White bread is not the healthiest diet, but a burger and fries every now and then is not a problem for a T1 diabetic whose treatment is under control.