Well, I don't think he had a secret agenda or anything. I think he was simply trying to be logical. After all, the Raposas literally just saw their friends sucked up in portals and they can't seem to find Mari anywhere. They don't really know of a reason why she would leave so suddenly either, Mari wouldn't just abandon them like that. Unless she fell off the Turtle Rock, the only other possible conclusion is that she was taken by Wilfre. I think I would've made that exact same assumption in his shoes.