Lee Hope is correct. A chain should NEVER be adjusted while the rear wheel is in the air, regardless the brand of bike. With that said, it can be done, but you have to put it to the ground, ride it, and check the tension again. Seems like a lot of extra work when adjusting it on the ground would be the straightforward process. Even when you do adjust it with the rear wheel is on the ground, it helps to get an accurate reading by pushing down on the rear suspension a couple of time to make sure it has settled, especially if the rear has been up.
Your handbook states you should adjust your chain with the bike on its side stand and in Urban mode. Use the tool in your tool kit to gauge tension. Your chain looks way too tight as your swing arm is hanging and chain will get tighter when wheel is on the floor. Only an observation btw.
In my experience it's quite difficult to adjust the cam mechanism to adjust the chain while the wheel is on the ground. The tension was double checked to be within speck once it was on the ground as well. At least in this case, that aspect didn't seem to matter, but I'll definitely look into that for next time!
