He has been talking about this movie for months. "How many months, Mom?" "I'm so excited to see Infinity War!"
The ending was very unexpected (I love unexpected endings). The theater stayed through the very end of the credits to see if there was going to be another twist. There was a scene, but it just confirmed the ending that we had just viewed.
The more I ponder, the more I really love the ending and find the movie even more interesting because of how it was left.