Higher for men?

Remember that BMI is based on the total body mass, and that muscle is denser than fat. (OTOH, that study corrected for level of exercise, and it's quite possible that the BMI that would maximize an average white American man's attractiveness if he's not allowed to vary his level of exercise would indeed be around 20.)

that curvy figures are considered (by many) to be attractive?

I am one of those “many”, too, but ISTM that in present-day Western cultures we're a minority; "thin" seems to have become a compliment. (Last year, someone offered to set me up with her roommate who probably had BMI around 18, and when I told her that I didn't fancy her, she retorted “but she's so skinny!” as though it was a positive.)