Humans were strange. Their presence didn't necessarily imply good, so Emery didn't jump in excitement when Elyn yelled that.
It was like, say, a rich man was stranded in the desert, with a bunch of things flaunting wealth. He was dehydrated and had multiple burns and bruises. He was there for hours and was on the brink of death. Then he saw a person in the distance approaching him.
With how unpredictable humans are, one of two things could happen.
The first is that the rich man got lucky and got someone who wouldn't rob him blind. And the second is the opposite of that.
Of course, there would be a third option. Stealing some stuff, and still helping the man.
The point was that humans were unpredictable and irrational. Even in a situation like this where they were all in danger, some people were bound to mess around with the mission because of personal vendettas.
Well, it all came down to who it was in the end.