That's misrepresnting the idea a bit.........the textbook "gutshot" generally involves a complete through and through of the body cavity. IMO there's a heck of a lot more damage done on an arrow that travels straight through the entire organ or organs (stomach and intestines) vs one that may have just grazed the outer layer of possibly the intestines for all we know cutting one small ribbon of intestine vs slamming headlong through the whole body cavity.

I don't see how the arrow could have passed UNDER the spine and that deer still be alive. right under the spine at that point lies the kidneys and the main vasculature. That arrow IMO isn't sneaking under the spine without killing that deer in seconds by severing the main artery or near side kidney.

I do also think it snuck over the spine (It tapers pretty good at that area near the thicker part of the backstraps, but I also do think that the arrow had to sneak into the body cavity a bit on the far side simply due to the shape and curve of the body.
Whatever is hit if anything apparently??...............he's doing pretty good.