Maybe I need to reread this a few more times, but I don't understand the crash, like how did the grandpa know they went forward in time?

Also Sengoku&co can't be clones like the animals, or the first chapter would make no sense, since they clearly remember getting on the plane and only a few of them flew off the plane (meaning like everyone else managed to stay awake during the crash, because Rion clearly remembered the first day they were there, were as Sengoku just woke up in the forest seemly after a day).