Public Practice at the Music Center = busking?

I suggested to one of my friends that he sign up to practice his cello at the Music Center as part of the Public Practice program, and in his reply, he wondered if people would then throw change into his case. Public music versus busking... what is the difference and does this kind of performing denote a "lower" kind of performance? It reminded me of the social "experiment" of having celebrated violinist Joshua Bell play in the DC subway on his priceless Stradivarius. He made about a dollar per minute with only one person appearing to recognize him. There is a lot to be said about context.