Weight loss is not linear; Is fat loss?

Honestly the two times in my life I have intentionally lost weight via calorie counting my weight loss has been extremely linear. Not sure if I am a special snowflake or if I am just trained on how to take reproducible measurements or what but yeah, pretty much an exactly straight line with low error in the measurements (+/- 1 pound).

You can see my weight over time for the last three months in a graph on my profile and it has been solidly predictable.