Even the most highly studied and trained music performers require a little overview before sitting down to play a piece from a legendary composer. It would seem silly for one to attempt to play the works of Chopin without any teaching or overview before hand. Amplify that thought even further at the notion of an 8-year old child trying to play Fantasie entirely impromptu.
Whereas you might expect this improv performance to be humorous and slightly embarassing for the child, it is not at all. Instead, you get to witness an incredible piano prodigy performing a work entirely without any previous training or teaching.
Jay Lewington sat down at this public piano in London at the St. Pancras Station. He taught himself to play through watching videos on youtube.