I just assumed Buster did buy the candy bar. We just didn't see him actually pay for it because it wasn't relevant to the main story.

I also noticed George eating the wrapper as well as the bar. I can't imagine that ending too well for George. He's going to end up in the hospital with not only a trienzomated zorn jelly addiction, but also an intestinal blockage.

Or maybe candy wrappers in the Arthurverse are edible. It cuts down on littering!