Normally, Diego would protest to being used as an errand boy. But these circumstances were NOT normal and he felt everyone could use a drink. The swarthy man fetches the wine and four glasses while listening to the Barathi tell his story.  He handed a drink to the Admiral, their guest, then to Dom. With that done Diego knocks back a drink himself. He didn't say anything though. He knew better then to interrupt the Admiral during a conversation.