After Matt and Joe use the balloons to send the phone up in the air to get a better view, Joe spies Trey in the video feed. There is a cut to the view as seen from a camera they left on the ground, but this shows that Trey has suddenly got the balloons that are still being used to float the phone in the air.
at 52 minutes the guys are blowing up balloons to mark their way back to the cabin. The balloons are shown floating upward. This would not happen with air from lungs, helium is needed to make the balloons float and no helium tank was present.
After the cabin window is broken, Matt says that birds don't fly at night. This is incorrect. Many species of predatory birds have a visual acuity that enables them to hunt, and thus fly, during hours of darkness. Owls being one of them.