Its a clever piece, an aptly demonstrates the point she was trying to make - that women are often pre-judged, stereotyped, by what they wear.
The issue - that of prejudging someone by the clothes they wear -apply to all. but for women the judgement often comes weighted with all sorts of preconceptions about their sexuality, which is not something that men need to concern themselves about, generally speaking. And it is prejudging sexual attitudes or availablility that would be considered offensive.
For our own personal interactions, we should attempt to avoid such preconceptions if we can, although prudence might dictate some caution when deciding how closely you want to get to a gang wearing say hoodies :)
Length of skirt a woman chooses to wear is entirely down to them, but there should be come consideration of practicality and aesthetics - Not everyone has a body shape that would look good in short skirts :)