Beats me. I would assume that it is sodium based on what I ate. If you eat 3 meals a day in restaurants you are eating a lot of processed food (i.e. sodium) versus eating the home cooked food where my wife does a better job of managing the sodium and everything is fresh.
I don't live in the keto world, I am low carb, high fat, which is close, but does not rely on being in some particular state. I call it lazy man's keto.