It's just general manners. A lot of people use "sir" & "ma'am" when talking to a stranger, trying to get your attention, asking a question, saying "thank you"... the list goes on.
Also, some children are brought up really old-fashioned & they are made to address their parents or any adult as "sir" or "ma'am", & they're so used to it, they continue doing it.
I know you're not old, but I'm sure you don't look like a young girl.
He probably felt like you were bossing him around. Or it said it jokingly after what he felt was a command.
its manors or sign of respect most of the time not much to go on to figure out if he is interested
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Perhaps he is just idiosyncratic, everyones different. Ask?
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