I just assume that about any battery powered product. Any claims are achieved in unrealistic perfect conditions, so you know the real number will be 30-40% lower. Even Apple does it.
There's simply no standard for testing. They can basically apply whatever "load" they want to calculate the runtime.
Manufacturers test their products under conditions that overstate real-world performance? Shit, my faith in capitalism is shattered!
I also overstate runtime when I am using my reel mower.