When he opened up his brain at the end.

Do pigs actually just eat people like that, or do they need to be trained to do so?
Pigs are omnivores - they're almost as happy eating meat as they are eating grains and roots. Wild hogs will go after lambs and deer fawns, so if given the chance to eat an incapacitated person, they almost certainly would do so.
There have been several stories in the news of domestic pigs killing and eating small children. A cripple in a wheelchair would be even easier to eat.

I've heard from people who are farmers that pigs will eat anything. It doesn't matter if it's living or not, as long as there is meat on it they will want to eat it. That includes people as well.

Well these pigs were trained.But i don't think pigs do that thou.Maybe wild boar idk

Do pigs actually just eat people like that, or do they need to be trained to do so?

Probably when Manson gets scared and pigs are about to eat him then suddenly sound goes off so you can feel empty and scared.