My 5 year old nephew told me "I know I'm going to have to marry you one day"

So I had to babysit my 5 year old nephew this weekend, and he was just playing around, but he started acting. Like he was my boyfriend, and he said "I know I'm going to have to marry you one day". I told him that we weren't able to do that because I was his aunt. He's not my biological nephew, he's my aunt and uncles son, so his dad isn't my dad, otherwise he would be my half-uncle I guess. I just found that strange. Is that something that most kids his age say?