If I'm not mistaken, most areas in the US have a 3-5 year age differential in those laws. So while it may list 16 as the age of consent, that's only if her partner is 19 or 20 years old... if there's a larger variance in ages then the limit is 18 like everyone is accustomed to.
I don't know if that's the law in EVERY state, but I'm fairly certain it is in SOME, and that site leaves out that little tidbit of knowledge.