Can someone explain Michael Hampton’s “thoracic” gesture line?

I’ve been reading through the book and looking over his Youtube videos and practicing along, but the bit that I get confused is when making the thoracic (spine) line. Sometimes he will draw it accordingly to what is seen in the reference, and other times he’ll draw the thoracic line in a way that doesn’t make sense to me, such as the pic for this post. I guess to put it in a dumb way, if the thoracic line is supposed to be the spine, why does it look like it’s drawn to look like it’s the side of the torso? Can someone who is familiar with this lesson break it down in a simple way? Thanks.

I’ve been reading through the book and looking over his Youtube videos and practicing along, but the bit that I get confused is when making the thoracic (spine) line. Sometimes he will draw it accordingly to what is seen in the reference, and other times he’ll draw the thoracic line in a way that doesn’t make sense to me, such as the pic for this post. I guess to put it in a dumb way, if the thoracic line is supposed to be the spine, why does it look like it’s drawn to look like it’s the side of the torso? Can someone who is familiar with this lesson break it down in a simple way? Thanks.