Apple Watch Move active calorie measurements inaccurate (too high)

My Apple Health/Fitness apps are reporting much higher active calories burned than expected. For example, I work in an office and have very little activity while at work. Today it is showing that I have less than 3,000 steps, but have burned almost 400 active calories.

Additionally, I have my Apple Health app linked to MyFitnessPal. In MyFitnessPal, I'm showing that my daily calorie adjustment for burned calories is only 45 calories.

Why are Health/Fitness apps showing such higher calories burned than expected while MyFitnessPal is only showing 45? And where are the 45 calories coming from?