Why was he calling me ma’am all the time and this one time he didn’t call me ma’am?

He’s a hotel worker and like 60 years old, he’s older than my mom and younger than my dad. I’m young enough to be his daughter. Anyway he always addressed me as ma’am when he ran into me, like 4 or 5 times already. Then yesterday he didn’t address me as nothing but did acknowledge me. Did I look old on the days he addressed me as that? Or did he realize I’m not as old as he assumed I was? I’m only in my mid 30’s.
Why was he calling me ma’am all the time and this one time he didn’t call me ma’am?
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