AITL for telling him he's not my Dad?

I (child, m) live with my sister (child, f, twin), our mom (ya f), and our mom's boyfriend (vampire, m).

my goal for my childhood years is to be a whiz kid, part of which means reading with an adult for a few hours. I wanted my Dad to read with me. My mom's boyfriend asked which book I wanted to read, and I yelled at him that he isn't my real Dad.

He tried to hide it but I could see a bit of pain in his face. I mean, come on, the guy isn't even human! How creepy that he's dating my mom! Maybe he's old enough to be her Dad or grandpa!

He looked to me though and pointed out that he'd been the one to help potty train my sister and I, changed our diapers, walked the floor with us late at night when we were restless so mom could sleep. He nursed us through every cold, ear infection, and even pneumonia once. He taught us to talk, he taught us to write, and read, he helped mom feed us when we were babies, he was even there when we were born and helped pick out our names, but he said I'm right, he isn't our Father, but he is our Dad.

At that point Mom told us both that she had been married once, but when she got pregnant her husband demanded she end the pregnancy. So she moved out instead, got a house with money she had inherited from her parents and hid from her husband. She then placed an add for a roommate, and that's how C came into our lives.

That can't be real though. Why would my real Dad not want me or my sister? Mom just answered with, "it isn't just the two of you personally, he doesn't like children. I don't know why."

I told her that wasn't good enough and she should've just gotten rid of us if we were such a problem.

C then told me, "neither of you are ever a problem. I understand you're hurting right now, finding all of this out but you will not disrespect your Mom like that. If you need time to cool off, go to your room until you're calm."

So now I'm asking, AITL for telling him he's not my real Dad? I know I probably am for what I said to my mom, but I'm not wrong about him, am I?

Oh and just to emphasize my point, here's some pictures. you can actually see the difference between us and him. We're definitely living, but he's more pale than pale. He's... almost grey?

C holding my sister, R so she can blow out her birthday candles

Mom holding me so I can blow out my candles