I'm a bit confused.  How is "queer" a gender? 
Could someone please elaborate.

A lot of people use "queer" as an umbrella term. It can refer to someone whose sexuality doesn't fit comfortably into the usual categories, but it can also refer to someone whose gender identity doesn't fit existing categories, in much the same way, I suppose, that someone can identify as "trans."

Some people use it as short for "genderqueer."