Is Apple Watch accurate in measuring activity? I just got my first Apple Watch and I notice the activity app tells me I've completed various goals at very strange times. I'm not particularly active. I exercise 15-20 minutes 3 times a week. But, I'll be sitting on my sofa late in the evening and I'll get up to get something from the refrigerator and my watch will tell me "Congratulations! You reached your goal for X!". I'll turn over in bed and it will tell me "Congrats, you reach your goal for Y!"

This happens regularly that in periods of doing almost nothing the Activity app tell me I reach my goal.

That got me thinking how does it actually work? How does it know me lifting food to my mouth is different than me living a weight? 

Is there any info on how accurate Apple Watch is knowing what the user is doing?
In terms of logging specific activity with the Activity app or third-party apps, I found it very accurate while using Apple Watch to train for triathlons.

For a passive activity like those you are describing, my understanding is AW is using the accelerometer together with HR measurements to determine activity and is not always accurate.  You can for example just wave your hand about to get a "stand hour" and I've noticed move data increasing while in the car. 

This is not a problem specific to Apple Watch though, all other fitness trackers I have had given similar issues. I think generally it will get better over subsequent OS releases as the AI is further trained and improved. You can dig into the detail of what it thinks has happened by looking into the Health app on iPhone, selecting the category and drilling into "show all data"