The hoped for mechanism of action of a ketogenic diet is hormonal correction, if a person is overweight due to chronically elevated insulin levels, a less insulinogenic diet addresses the insulin response to food, and the decrease in liver glycogen makes for a lower fasting insulin as well. You can only really expect a correction if something was wrong in the first place. Since you're not overweight to begin with, odds are that your insulin wasn't particularly elevated. That's just playing the odds, there are exceptions where people get type II diabetes or insulin resistance without being overweight, but they're pretty strong odds.

Higher early losses generally occur in people who are overweight, partly because they're more likely to have excess water weight to lose. People who start out leaner can't really expect this. Early water weight is often put down to whole body glycogen stores, but this can only really account for four pounds or so, and that would involve the water associated with the body's entire glycogen store, that's beyond what actually happens. Most of the liver glycogen might be lost, that accounts for about a pound. Most of the water loss people report has more to do with shifting hormones and a reduced retention of electrolytes, than with glycogen.

We're mostly water, shifting water balance can easily mask fat loss, if you don't carry much excess water, this might show up on the scale earlier rather than later. One of the more common complaints here is people losing weight for three or four weeks, and then stalling. It doesn't mean they're not losing fat, it just means that if they are, they're just regaining enough water to compensate for the lost fat weight. That can be good, sometimes it's due to muscle or other lean tissue gain as opposed to just taking on more water.