Love this original story. And she may say it was no big deal as brothers don't look at sisters that way, but I and many others can assure, under those circumstances, WE DO
I think it's very unlikely she did not understand he was interested in seeing her, but saying he was not interested allowed her to parade around naked in front of two very focused young men whenever she wanted! And she says the same thing today as she doesn't want her husband to think she's some sort of "pervert".
In the family exposures thread I wrote about a college GF who did the same sort of thing around her kid brother- pretending to be innocent or unaware of her exposure, but doing her best to show him as much as she could, every chance she got!