I don't think I've ever seen a video of this move. I'd never heard of it before NROL either. So I think the book's description may be all you're going to get!
Or you could video yourself and we can tell you if we think it's right or not.
nope thats not what is in NROL. What is in NROL is front foot on a step back leg split like in a split squat. Then do the good morning. Those in that video look really scary.
He calls that a "single-leg good morning" but it looks just like a barbell single-leg RDL to me. At any rate, it's not the split good morning from NROL.