He was probably dead when he fell in. It looks like only his head and hand, and part of his chest were submerged. Looks like he keeled face first into the drink, yea. They don't typically eat people unless they are dead or drowning. It's the thrashing that attracts them, mostly.
ya ur right about just his upper body being submerged...but they just kinda ate him all the way through from that spot cause when you look at the photo hes bare from everywhere shown from the autopsy incision