No, its a matter of thighs ._. You can be thin and not have one, you can be chubby and have one. It depends on how large your thighs are. And though wait and bone structure has some to do with it, it all comes down to your thighs... I know, I'm a girl, and I know many other girls.
I'm a girl and even if you are skinny, your bone structure [and muscle] determines whether or not you will have a thigh gap. Now sure, you can obtain a thigh gap by serious dieting and lowering your body fat percentage, but natural thigh gaps [aka not dieting to lower your fat percentage and muscle mass] are entirely based on your bone structure.
Naturally you want to have a healthy fat percentage but if your bone structure and muscle doesn't give you a natural thigh gap, you have to go below the healthy percentage to obtain that look.
You should take a look into many popular tumblr posts about thigh gaps and the facts behind them. Many even show you simple stances to give you a false gap which is what most of these popular thigh gap pictures really are.
You are like the first person I have ever seen to not draw style A O_O It's very unrealistic I think. Every photo I have ever seen there is a curve for the hip, then the leg, not one big curve for both!
Never realised that the base was actually my leg and not part of my hip, but now that I've seen this, it makes a lot more sense! I don't draw humans, but this is a really cool tutorial just looking at the structure! Very informational and interesting.