This is considered dirty fasting, yes.
It might be “dirtier” than you think. 3-4 cups with milk in each one could add up to a lot. I know you said 30-50 calories total. Whole milk is 9 calories per tablespoon, FYI. If you’re having more than 1 tablespoon of milk per cup, it could add up more than you think. (Measure it out to make sure.)
Dirty fasting doesn’t necessarily totally ruin all fasting benefits. Your insulin is still probably lower on average than it would be if you were eating meals/snacks.
But it would be better to drop the milk — or keep it to only one cup in the morning, if you must. Consider switching to tea the rest of the time; lots of people find that easier to drink black.
Also, have you tried cold-brew? I always found that a lot easier to drink black. You can heat it up if you want a hot drink. But the low-temp brewing process makes the coffee far, far less bitter. Easy to DIY — put ground coffee in cold water, let soak 8-24 hours at room temp, then strain. People sell special cold-brew devices, but you don’t need them. You can use a French press, or literally just a jar/glass/tupperware and strainer.
Dump the calories stuff.
Why?
Not all calories are the same. Foods are processed differently.
We have no idea how many calories we will burn from day to day. Sleep, stress, periods, ghrelin, leptin, cortisol, insulin. Etc.
We have no idea how many calories are in our food. 20% error rate.
We sometimes absorb fewer than the calorie count. Some food calories are fully utilized and some aren’t. Gut bacteria thrives on some foods only.
2000 is way too high for a 4 hour window, even if you were fasting properly. Stick to water and herbal tea with OMAD. You may as well, your window is already small. Keep your meal to 1000 kcal or less, and make sure it’s got a lot of veg. It’ll melt off.
Deep autophagy is easy to short circuit (I think it is as little as 3 grams of the protein leucine can stop it) but for regular ketosis it should have not affected much. This is funny; if you must switch to heavy cream instead of milk.
Also don’t account for the calories that your fast takes care of. If you eat 2 meals a day and your maintenance is 2100 calories (to make the math easy) your fasting ‘maintenance’ (the calories you need to refuel and make your body happy while still loosing weight to fast) are 2/3rds of that, or 1,400 calories; you are still burning 700 calories a day without your body risking a metabolic drop from caloric restriction. There are some fasting efficiencies that work on your favor and it would still work if you eat a bit more.