In Chapter 1, why does Stilton take issue with Bertie having a drink?

In Chapter 1, Stilton arrives and sees Bertie is having a drink which displeases him. Stilton has drawn Bertie's name for the annual Darts sweep at the Drone's Club and so stands to win money because of Bertie. For this reason, Stilton takes a judgmental interest in Bertie's conduct.