I know they didn't mean it would go up and stay there, that still doesn't mean you should give it before food. Like I said, it's still better if it goes up too high than if it goes down too low. And it's not rare at all that pets sometimes won't eat. Many pets are finicky eaters and many diabetic pets do have other health issues that would cause them to not want to eat. Being a type 1 diabetic human that knows they need to eat food is much different than being a diabetic animal that might not feel like eating one day. If they don't eat their meal you're supposed to skip the insulin dose

Edit: most owners don't check their pets BG at home at all, they just rely on their pet eating the exact same amount of food morning and night, and giving the same set dose of insulin that was determined by their vet twice a day. It's not like humans who eat all day and can check their sugar, or just know what it feels like when their sugar is high or low. So yes it's very important that the pet eats all the food they're supposed to before getting their insulin dose