I can't say as this is terribly shocking... first the heart rate monitors on these devices are never going to be terribly accurate... there's a number of problems inherit with the design, but they are okay for basic general use.
The sensor is designed to detect changes in your capillaries as blood is pumped and figure out heart beat rate based on that. But this is assuming there the sensor is in contact with your skin. If it isn't, there may be any number of things effect the reading. Looking at your video you were moving the watch around and at times had it positioned over different colors carpeting (it appeared). I suspect these things contributed to feeding odd data to the sensor, which it used to figure out a heart rate.
The Sensor only does what it's programmed to do and then feed the data to the software which interrupts the data assuming it's genuine.
For example: Pregnancy Tests... they tell women if she's pregnant or not... well... no, they actually don't. A pregnancy test looking for certain hormones in a woman's urine. These hormones are only produced when a woman is pregnant. The "sensor" looks for the hormones. If it finds them, it singles to the "software" in the sensor and the "software" reports to the woman: "You are pregnant!"
But here's the interesting this: If men with a certain type of cancer urinate on a pregnancy test, they will get a message saying they are pregnant! So what gives? The "sensor" saw the hormones (caused by the cancer) and feed that info to the "software" which then reported to the user: "You are pregnant!"
In the same way the heart rate sensor on the watch is getting weird bogus data that looks, for whatever reason, like heart beats. Just like the pregnancy test peed on my the guy, it assumes the data it's receiving is genuine. Then the software, just like in the pregnancy test, assumes the data it receives it genuine and reports on it.
At least this would be my best guess. I supposed I'd try to take your pulse with both the watch and manually a the same time (or nearly so) and see if they are close. If they are wildly off, then it might be a bad sensor. If they are close then I'd suspect a good sensor, just getting weird data when not on your wrist.
