My crush called me ma'am?

I like this guy and I think he likes me back. We haven't dated yet. (On a side note: he is in the marines if that has anything to do with it). We are both in our early 20s. I sent him a good morning text. And he replied with "good morning ma'am" with a smiley face emoji. It threw me off because it made me feel old and like I was "friend zoned". So if a guy liked a girl, would he ever call her ma'am? Is it out of respect? Or is he being sarcastic? Or am I more like a friend/mother to him? Why did my crush call me madam?

My crush called me ma'am?
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