I don't see anything wrong with it as a voluntary learning presentaion, although there was a sort of circus-style atmosphere present in the crowd ( they should have been more quiet to respect others in the audience). Nature is nature. Snakes eat things. Big snakes eat big things. Also, they could watch as the rabbit traveled down the digestive tract ( the lump in the snake) and discuss the food chain, digestion and metabolism if the teacher wanted to take it even further as a learning tool.
No one was forced to watch the feeding, and anyone who does not like to see this does not have to watch it and then complain about it afterwards. That is like going to see a known horror movie and then complaining later on that you dodn't like horror movies. If you don't like, don't go. Basic truth: snakes are predators. They eat other animals. Being in captivity does not negate this basic truth. Nature is not always pretty ( it often isn't). Many snakes will not eat dead food, as well ( some will, and that's nice... but it isn't the case often times). The teacher should not get in trouble for teaching. The only thing that should be stressed is safety ( no students/etc touching or approaching the snake while it is out of its enclosure, etc...).