It sounds like you have used ground/mince beef that was too fatty and the fat has rendered out into the casserole. I tend to avoid low fat beef as we want plenty of healthy fat to keep us fuller for longer and all the benefits that come from a high fat diet, but I also avoid the highest fat beef as too much fat comes out in the cooking process for a dish such as this one.
A ketogenic diet helps control blood sugar levels. It is excellent for managing type 2 diabetes, sometimes even leading to complete reversal of the disease. This has been proven in studies. It makes perfect sense since keto lowers blood-sugar levels, reduces the need of medications and reduces the potentially negative impact of high insulin levels.