The only
video i saw on the install for that AIO was from GN. I'm not sure why it ended up off-axis like your picture, I'd be concerned too. My only suggestion would be to take it apart and take pictures of everything to see if anything looks off before installing. Theoretically, it wouldn't hurt performance much anyway, as long as the pressure is good and the contact over the chiplets and controller are good (which are all towards the bottom of the CPU in the image, so the slight rotation wouldn't really be an issue, it just doesn't look as good as you'd want it to). The one thing that always helps when installing a CPU cooler is to lay the case down on its side so that the CPU is flat when you're installing the CPU and the cooler. It's easy for things to slip and be off-center when trying to install it all vertical.
Edit: Also, the way the cooler's VRM-fan snaps on top of the pump there (on the CPU), it will likely mask any slight rotation in the mount. Edit2(sheesh sorry): I apparently missed the part of your note that said "or securely mount it down". This sounds like what GN showed in their video. I would echo my previous statement about laying the case down while installing it so that you can push down with your screwdriver and make sure the screws thread into the bracket properly. It looks like it's really easy to only get 1-2 threads in, then switch to the other side, then have the first side pop back out. You'll want to make sure you have enough threads engaged before swapping sides that you don't pop out of the threads. I could see this being an issue the way they make you thread it with the screws under tension, and even damage the threads possibly. Hopefully that has not happened for you.
I agree on rotating the radiator so the tubes come down on the left side of the radiator (from the picture's view). I had to do similar on a build at one point. I even moved my rear fan to outside the case, which was not ideal lol, I don't think you'll need to do that.