I couldn't tell you how many bearings I have packed with that packer ,now not sure what you mean doing it right . I can only guess which position you have the bearing inside the packer , seems self explanatory to me . Have never tried them one way or the other ,I always position them the same way in the packer , not sure if there is any instructions on how to use them, I would have to think there is . It's been too long to remember . But It's obvious when using the packer ,and seeing the grease push out, from inside , as that happens there is as much grease as you possibly can get in a bearing. Also it will tell you as soon as that grease starts to push out how well you cleaned that bearing ,you will see the old grease push out.
I know there are probably many that think hand packing is the only way, I was certainly one ,until an old guy years ago told me about them, had no idea. You couldn't get me to hand pack a bearing now . Prove is always in the pudding . I have packed car haulers ,fifth wheels ,many boat trailers ,utility trailers , box trailers , not a bearing failure in the bunch .
Preload is important on tapered roller wheel bearings, I could get into the real sophisticated way using a torque wrench , preload to a certain value ,back off retorque to a certain value ,but not sure how many do that. I have always snugged them up while turning the hub ,and then backing them off , and retightening to a feel , with no play. Don't know how many times I have been caught in-between what I like , and not being able to get the cotter pin in . I usually error on the side of a bit more loose than tight , just depends on whether it creates any slop . If there is I will go a bit tight , then run them to see how warm they get .
What I found over the years ,use a quality grease ,inspect the bearings ,and race for any issues , new seals , and pack ,and preload properly , and you are good to go . Thats why that video is terrible, and hopefully no one follows that . I have seen some YouTube videos that were bad ,and that one ranks right among the top ones .