u/Key-Row-2701

In the "The Flight to Neverland" score by John Williams, about 20 seconds in there is a phrase in G Major that he somehow ends with a B Major chord, then he goes straight back to G Major. How is he able to just smush together two seemly random/unrelated chords? I'm assuming it is just voice leading or something but want to hear your thoughts. Here's the score: https://www.youtube.com/watch?v=23mtFUJP_48