Ok, he was tired after work and not really thinking about the implications of watching a show like that with a 4 yr old... But since the the can of worms is already opened...
Small children tend to attribute human characteristics and feelings to animals... Which explains why they bond so well with stuffed animals. My concern if it was my daughter would be that I don't want explaining this topic to undercut the development of her empathy and consideration for other's feelings. So he should be prepared to be patient with the topic...
Here's a link to a childrens book on Amazon that discusses the food chain: http://www.amazon.com/Chains-Lets-Read-Find-Out-Science-S...
Here is another link to a webpage that discusses why we need food: http://www.feedingminds.org/level1/lesson1/obj1.htm
Of course, the book is geared for ages 5-8. Your son should use his most sensitive paternal judgement on whether she is ready for more information on this topic. Ultimately, he doesn't want her to start waking up with nightmares...
When my nephew was small, he suddenly asked "Why does chicken have bones?!" That freaked my sister out because she really didn't want to have the food chain talk with him at that age. My husband and I decided to try and avoid that issue by calling meat by the 'butcher name': poultry, pork, beef, venison... Hardest to do with poultry because everyone calls it chicken. One day, I accidentally asked my 2 yo if she wanted chicken nuggets and she started making chuckling sounds... (uh oh!) So we're trying to be more proactive in calling things by their meat names instead of as farm animal, hoping that will distance the topic.
Good luck.