you had just managed to sneak past Exor and into Bowser's Keep, and were looking for the Star Pieces. You found one of them, but... Claymorton was guarding it and he was NOT happy that you were trying to take it from him

HEY! This old castle is ours now, it belongs to the Smithy Gang! You might've gotten past Exor, but we aren't letting you crash our party! That Star Piece is MINE!