That's exactly the point. How about if she walks over a sewer grate? How about if she's walking down a set of stairs?
This court really had no choice but to come to its conclusion (which is why it was an 8-1 decision). The law by its nature is an attempt to apply objective legal standards to something that is littered with degrees of subjectivity.
She had dressed so that she had the reasonable expectation of her private parts being covered.
If she was wearing pants you'd be right, but you -- and the legal authorities, more importantly -- have no basis to determine exactly what anyone's "expectation" was.
You can’t capture that shot unless you go out of your way to do it. (excepting the situations we have discussed)
If the perp used a devious method to facilitate the capture of a photo of a woman’s private parts, it would be a given that his actions were clearly intended to invade her privacy.