Language confusions

Just yesterday I found out that phrase "looking smart" has two meanings. Several days ago i was wearing a costume to my work and my boss who saw me entering, told: Wow Olga, you look smart today! I didn't connect his comment with my costume and thought to myself that, what before he thought I wasn't smart? And instead of thanking him I asked my boss what did he mean exactly. He looked at me, smiled and said that my costume is very nice. So I thought: what???!! ok, whatever... just let it go.... Yesterday Philipp after booking a table at Landmark said that people who come there usually dress smart. And then I finally got it :)