[Plugin: Posts 2 Posts] Custom meta box: WP_Query call vs get_connected()?

Working on a custom meta box using the P2P core. I noticed something while experimenting: I tried using the WP_Query example and got 0 results, but when I used the get_connected function, I got the results I was looking for. Is there a reason why that is?

http://wordpress.org/extend/plugins/posts-to-posts/