I don't think it's willgoo's fault, they're just doing a mockup using the images that GPD provided for them. The size comparison between the hand and the device, plus it being pocketable don't add up - the device should be much smaller than it is now for all of it to make sense.
Regarding the screen size, they didn't take into account the dead zone around the screen. I think it's an honest mistake stemming from the screen being turned off in the GPD images.
I recommend not pre-ordering this device either way, too much conflicting information. It doesn't really matter, though - it comes out in a month or so. You can make a better, wiser decision once it comes out.