If, as you say, you are extremely inactive, the watch will be more sensitive to changes in that inactivity. Anything that elevates your heart rate may well trigger credit for "exercise" because you don't do much. So if you are extremely inactive, almost any activity will trigger an increase in your heart rate, so the watch sees that as "exercise." And if you are moving your hands in your job, you may get credit for "steps" because the watch is looking for a certain kind of motion associated with walking. It's pretty hard NOT to walk 1-3 miles in any day. Even on my most lethargic day spent on the couch watching TV (usually Sunday afternoons), I still get about one mile of steps in just around the house. And 200 calories is not much to get credit for, either, if your hands move in your job.
So, it doesn't sound like it is malfunctioning to me. But if you think it is, take it to an Apple store and have the Genius look at it. They don't have much testing capability in the store, but maybe they can simulate something to see the the sensors are working properly for you.
