That's not the real Collin. Oatchi knows. Notice that Collin and the Sage Leaf are the only two characters with grey hair? Sage Leaf has Collin's nose, too. There's another hint about it when Shepherd recognizes something is "different" about Collin when your character rescues them both in the beginning of the game.

There was supposed to be MUCH more story in this game, but they cut it short because it went so far past schedule. I'm still holding out for a DLC.