PM, the dude fit through the door and was able to enter the plane. That door is the closest emergency exit for the first class cabin in a 737 (which is what Alaska flies)… I assume he can exit in an emergency the same way he came in. But gosh I felt sorry for the window seat passenger sitting next to him… Imagine asking the guy to let you out and back in to get to the bathroom? 
I would not worry as much about Kajon’s improvised seat divider as I would worry about someone’s large iPad becoming a projectile!