Yes, there is foreshadowing in the book. Foreshadowing is when the author gives you hints early on that something will happen later.
First of all, at the beginning of the book balloon travel is said to be good when you are not sure where you are going. This foreshadows the fact that the balloon will go to an unexpected place. This also foreshadows the escape with the balloon.
Second, when Professor Williams begins his speech, we already know that he survived the journey. Otherwise, he would not be alive to talk about it! The rest of the story is told in flashback.
Third, when he crashes we know that it’s a volcanic island. This foreshadows trouble and danger, especially that the volcano might erupt (which it does). Also, it seems that strange things may happen on this island.
Finally, when we meet the unusual inhabitants of the island with their quirky rules and diamonds, we know that something is going to happen to them.