30 years old, diagnosed with stage 2 breast cancer, breast cancer hereditary in family, try my best to eat healthy, did my diet bring this about?

Absolutely not. Anybody who told you that your hereditary breast cancer was "caused by your eating wrong" is at best "misled". I'm sorry you have cancer. Nobody can stop "entertainment" / "junk" sites from making stuff up about diet and disease; most of what you read is lies. But the best scientific studies show little or no link between breast cancer and food choices. Trust you've had BRCA genetic testing.
No. I'm sorry to hear about your cancer. I hope you are doing well. Risk of cancer comes from genetic and environmental factors. There is no way of knowing exactly what caused your cancer but I suspect that genetic predisposition (family history) played a large part. You should follow the treatment plan recommended by your cancer doctor. Try to eat well and reduce stress. Do yoga or exercise weekly.