Looking at the video, it seeems that the mount is supposed to be a pressed fit???? Otherwise, what would keep the motor from coming out in flight as Lt smash stated? Is there a set screw to keep the motor in the mount? Like a grub screw? Or is it just pressed in to hold it? If it's just pressed in, then it should be a very tight fit to keep the motor in. Just an observation..............
If it's press fit, the mount would need to be installed PRIOR to installing the motor on the plane, because you definitely don't want to press it in with the mount on the plane first.
Once again, i'm just making an observation based solely on your video, as i'm not personally familiar with this product.