You saw it right. Finch was about to feed the bait to the Tiger Shark, but the Lemon Shark was closer to it, so he pulled his hand out of the way. As a result the Tiger Shark ended up biting the Lemon Shark on the nose.
Timing is everything. Typically when the Tiger Shark opens its huge mouth, a water suction occurs. Finch would feel the rush of water flowing into the Shark mouth. All he needs to do is to release the bait a few inches in front of the Shark mouth. The bait then would just got sucked into the Shark mouth. If you release it too soon, before the rush of water flowing into the Shark mouth happens, then the bait would fall off to the bottom and gets eaten by the other quicker scavengers. If you release it too late, then your hand might get eaten by the Shark.
Finch still has all of his fingers. So he's an excellent Shark handler / wrangler and has quick reflex and good timing. I have seen some of these guys with missing fingers.