!! is a trick in languages where values other than false count as "falsy" in boolean operators, like in ruby if you have a value that might be nil you can explicitly convert it to false with !!. so if you are a-gender, or anti-gender, or have some other value for gender that doesn't count in some sense as the affirmative presence of a gender then !!gender makes it false. and in my experience at least, for some cases like that, individuals do self-identify as trans and in others they don't.

certainly i fit that description myself and i do self-identify as trans in contexts where it's safe to do so