How original, picking on the pettiest of things like an absent question mark because you have nothing else to work with. My god, just when I thought this couldn't get any more pathetic, this thread sinks to a new low...
I would say that you are entitled to say no even if something is within your levels. If I'm approached by a nude/glamour photographer I make sure in the communications before the shoot that the style they would like to shoot is the same style as images on my portfolio - if they suddenly bring out rose petals and ask me to lay on a bed while looking "sexy" then I would say no. There are many models who will just shoot whatever with whoever is paying them but i have always respected those who stick to their guns. Why shoot something you are not comfortable shooting or don't like?! it's hardly going to make you enthusiastic during the shoot if you are doing something you know will not suit your look.
Regardless of if you have concealed nudes on your portfolio you took the booking on under the illusion that it was a fashion shoot - wearing a dress. If he was going to photoshop your "bits" out then surely a bit of tape wouldn't make that any more difficult.
I think you did the right thing and the best thing is from all the negative experiences we learn. Many models would have turned up and felt "obliged" to shoot what this person wanted so I'm glad you didn't. Hold your head up high!
I tought in HE for decades and can well appreciate your frustration. But, remember students were born, went to schools, then Uni as an unbroken stream of womb-like existance and have no conciousness of real life outside the school/college/uni gate. Most are OK, a few are brilliant and a few you wouldn't let wash your car. You seem to have encountered a non-car-washer. In future help out friends and collegues and let the others learn for themselves.
I can't say that my levels have ever been pushed - I've been firm from the start with what I will and will not do, and who I will or will not work with. He miscommunicated, which gives the model the same right to leave a shoot after attempts to negotiate back to the original communicated idea fail as it would if the situation was reversed.