The need to disclose

Sigh.

I've been talking to a guy on IRC a bit. He's local and likes fucking girls in the ass. Since I like getting fucked in the ass we bonded over it.

Since it's a text based chat, and I just said I'm female, he assumes, naturally, I have a vagina and all the normal girly parts. I don't think I'll ever meet this person at all, so is there a need to disclose my gender status to this man? I feel like I'm lying. But why?

And why do I feel this need to tell him that I really have a dick? I don't plan on meeting him, and I've only told him the truth about me...

This is just another thing to add to the list of things that make me insecure about having sex.