A lot of BB's preach good form, but i've seen videos of Jay, Viator, Victor Martinez etc all training with sloppy form. I think we all cheat a little at some point or use less than brilliant form. However momentum can be a good tool for shocking a muscle. I've found this with cheat curls and calf raises etc.
I know I wasn't there - or even born - in that era, but you do get a warm nostalgic feeling looking at footage that old with athletes that good. Maybe it just reminds me of when I started lifting, who I was inspired by, who I wanted to look like as well as remembering the good people I've trained with over the years.
Boxy waist or not, Arnold was a legend.