Why did he ask me if I was on my period when we were planning on hanging out?

iv'e hung out with this guy twice before. we were planning on hanging out. he asks me "are you on your period"? i said why and then he said just wondering. does this means he wants to have sex? why would a guy ask if you are on your period? i was not moody or anything so i know he isn't asking because of that.
Why did he ask me if I was on my period when we were planning on hanging out?
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