well, nothing too special about it. When a showgirl with short dress/skirt sits onto the bonnet of a car, surely will expose. They usually wear some form of shorts etc beneath. They'll know that they're 'exposed', not that they'll do it on purpose, but the situation will arise more easily for certain poses.
This goes for organised model shoots. Sometimes a model wears a short skirt, and when photogs ask the model to sit down at some low height, surely will expose.
While one 'should not' seek to capture such exposure, there's nothing to stop a male's hormones from telling its host otherwise.
I'm just glad that no one has posted those pictures here or at other forums (that I know of).