Calorie tracking

For all you Apple Watch users, I need some help. I just spent about an hour and 20 minutes raking leaves, my heart rate got up to like 180 at one point (possibly more than once)… it was quite a workout. I didn’t track it as a workout. My watch says I’ve only burned 180 calories for the entire day so far (it’s 10:50am here). If I were to have started a miscellaneous workout before raking the leaves, I guarantee my watch would have told me I’ve burned many more calories than 180. Does anyone understand why this happens? The same amount of physical activity, yet calories burned are higher when you “track” activity rather than just have the watch on while you do things.