A very good on his part that he fulfilled the request of the little lad. The 10-year old kid asked Dave to let him play with himself when Dave was talking with the crowd while standing on the side of the stage.
Dave asked him if he knows how to play guitar and the kid replied with full enthusiasm and said "A lot of Metallica songs." After performing 'Enter Sandman' together, Dave gave the guitar to Collier.
1 Here's just a Metallica appreciation meme collection from Imgur to amuse you: