Ketosis has nothing to do with calories in. It's dictated by whether your body has glucose/glycogen available to run itself. If not, your cells start using fat directly and your liver produces ketones for the brain, which it uses with the remaining glucose in the blood.

The person I was replying to specifically mentioned that they went on a keto diet.

Ketosis is different than ketoacidosis.

Right, but being in Ketosis is a precursor to ketoacidosis

You have to be doing it really wrong to get there though. OTOH it's always a good idea to research it before starting something.