Does the phantom 2 compass receive as much interference from a metal environment as the phantom 4?  I'm asking because I saw some guys flying one inside a metal cargo hold of a ship.  

The main thing is you don't want to calibrate a compass near a lot of metal.  

Here's a vid you might find interesting.  Be sure not to miss the part at 1:03 where he flies inside the cargo hold of the moving train.  

https://youtu.be/-JvETIQMRks

I saw this and it looks like a p3

I would not recommend user fly in that way. It is too dangerous. For your question, Phantom 4 will have a better anti-interference ability than Phantom 2.