When the winged man-thing came out of the jungle and started talking to them, Jim knew the logbook page was true.  He literally jumped in surprise, and when the other girl came out of the jungle and did... whatever she did with electricity, he remembered that other line from the page.  Developing strange powers.  It was then that he realized he, himself felt kind of strange. It wasn't anything he could put his finger on... until he realized contact was the issue.  His feet weren't touching anything. He looked down, and indeed, his toes were a good half inch, at least, from the surface of the sane, and just hanging there.  Apparently, Jim could fly!