After the food was gone, Ian still wasn't ready to leave. He instead had taken to smoking and requested more alcohol. There was some reason that he wasn't ready to leave yet. Houston just didn't know what it was.
After the last comment that his boss had made about innocent people losing their lives, the conversation had died off. They enjoyed the rest of their meal in silence. The detective at first had thought it was because the other was enjoying his food too much to be bothered with talking. Now that they were done though and the conversation hadn't picked back up, he knew that there must have been another reason that he wasn't talking.