It's his right. His gender identity is his own business. He has the right to self-determination and if it's convenient for him, no one has the right to forbid him. But if he leave his "twitter account", in his posts, where he on a photo with a beard and drinks beer - then let him not complain later. This is considered gender cheating on any respectable forum, and sometimes even trolling
You know this yet you went on to cause a ruckus about their gender. Personally I don't see it as much of big deal trying to reveal one's gender or force them to accept what they know since this place is anonymous and its a personal choice of the individual if they want to say it out or not.