The body creates glucose from just about anything. Your brain ONLY runs on glucose. If you eat only protein, your body converts some of it to glucose. If you eat only fat, your body converts some if it to glucose. If you don't eat at all, your body breaks down your own muscle and fat to create glucose. Your body creates glucose out of whatever is available.
What your body can't do is turn carbs into proteins or fats. That's why carbohydrates are not an "essential nutrient" like protein and fat are. And while plants do contain some proteins, none of them contain all 9 of the essential proteins. Only animal products contain all of the necessary proteins in a single food source.
Blood glucose will vary day-to-day though. You can't tell much from a single fasting glucose reading. Sometimes it will be fine, other times it might be elevated. A single reading isn’t enough to make a diagnosis. You have to see what it's doing over time. An A1c is basically a "3 month average" glucose reading, but it isn't limited to fasting only. So it may indicate that on average you're fine, but you could have big peaks and valleys which aren't good either.