Calling me "sir"

[JovanD]

I held the door open for a average sloot today and she said "thank you sir". She treated me like I'm someone would treat their elderly grandfather. I'm only 22 I would gues her to be about 19. Was she trying to patronize me or was it a genuine sign of respect?

Id say it is sighn of good manners, it is acceptable to say sir to stranger.