As far as I know, sir refers to a male supervisor. Then what's the appropriate title for female supervisors?
Actually, "Sir" is not just used to refer to a male supervisor. "Sir" is a polite way to greet a man and not necessarily even used by many people as a way to greet their supervisor (who can sometimes be called by just their name, depending on the situation). In the case of this video, it has been used as a way to politely refer to a man. For women, you can choose to use "Miss" (for younger, unmarried women) or "Madame" (for older, married women). Ex: Hello Sir, how can I help you today? Ex: This Miss appears to be lost.