I was wondering too...I was just on my phone going through google image search and this thing popped up...the comment was written in Russian- "This is what happens when you use arrows not suitable for your bow"...so my first guess was "underspined arrow" and as you already mentioned a lefthanded grip on a right handed bow...
as seen how arrows break in slow motion (2:12)...this would be my first theory...I'm still looking for the original post cz I kinda lost it.
Another theory is that the bow was overdrawn and the arrow tip stuck in the bow, therefore after release the arrow just snapped leaving the part with the fletching nocked and continuing towards the archers hand...I'm also wondering if it was a recurve or a compound he was shooting...perhaps a malfunction of a homemade dropaway rest.
PS: This is a creepy post...so... here's something to lighten you guys up...a somewhat comical paradox...one of my childhoods
favorites.