Whose Story is it Anyway?

At a recent writing workshop I attended, the subject of multiple POVs came up. On my newest WIP, if you remember, I'm going with the dual POV, first person. At least thus far. Anything is game in revisions, right? It could be one POV third person by the time I'm done.

Anyway, one of my workshop buddies mentioned no matter how many POVs there are, there can only be one main character. It is one person's story. And he pointed to screen writing as an example. Think LETHAL WEAPON. Whose story is that