So everyone has fat
What do people mean
They mean that if you do not have a lot of fat on your body than longer term dry fasts can be dangerous as your body will have no fat to consume as energy.
If your are Very thin then it might be advised to put on some additional weight before an extended fast.
If you are new to fasting than you probably don’t want to go more than 1-2 days your first few times so it should not be an issue yet.