Dunno. My best guess is people read the aunt being "traditional" and decided she must be a monster even though sneaking off to fuck in somebody else's home is weird and disrespectful and no reasonable person would expect to find you doing it. Especially when they don't know you're with your significant other and especially when it's family.

I used to actually live at my grandfather's. As in, it was my actual home for awhile. I still wouldn't go back to my old room there to sleep with my girlfriend at Christmas or whatever.

A lot of people on this post either didn't read it very well or are really weird about where they have sex.

I think the person who decides to have sex in somebody else's house needs to worry about boundaries. Especially her grandparents.

I agree with you if OP was in her own home which she wasn't. She was at her grandparent's and was in the room she used to stay in. She was at somebody else's house during a family gathering. Aunt had no reason to assume she'd be having sex at the time because who does that at their grandparents' place?

She's not a busybody. She didn't know they were together in the first place and OP was the one with the bright idea to fuck at her grandparent's house during a family get-together.