Thicker Than Your Average?

So, I went to work out with my trainer last night and he wanted me to do some crazy ass ab work where I lay on my back, hold my legs up 6 inches from the ground and then draw the alphabet with my feet. He showed me the example and I asked him what was really going on. He explained and I told him it looked crazy and that I was going to have to take a pass. He rightfully agreed that I could. When I got on the bench to do our usual crazy 6 inches like abs, he told me to be careful b/c I have an "insane" arch in my back. I was like "what?" He went on to explain that he could slide his entire hand underneath my back when I lie down b/c of the arch. Which is true, but as I explained to him, not uncommon for most women with some curve in the back. He agreed but looked as if his heart wasn't really in it which led me to believe maybe this is not normal or average. That is weird to me. I have a pretty good relationship with my body and I don't find myself to be ridiculously curvy. No, I am not shaped like a boy, but I'm not shaped like Melyssa Ford or Kim Kardashian either. And if I was shaped like that it would be great, it's just that I'm not. So it seems crazy to me that my trainer is acting like I'm all Jessica Rabbit or Buffie the Body. If I were a seventh grade boy I would say "arch deez." But I'm not and I really can't think of a better comeback at this time, so I'll just stick with "whatever."