Crush became friends with my brother? What does this mean?

maryelizabethhx
So I have a crush on this guy at my school, let's call him T.

My brother Derek, who's a senior, is with me frequently because he's like a friend to me. My crush has seen me walking around with my brother before and once when my brother was alone, he asked him, "Isn't Ally your sister?" and Derek said yes, and from then on they were friends.
Note that they weren't friends before my crush questioned him.

My brother said my crush is kind of a kiss-up to him. He has no idea that I like him.

How do you think he knew that Derek was my brother? I never talk to my crush, but we have lots of mutual friends. And why did he become friends with him?

Something like this happened earlier in the year, this guy named Chris asked my brother who he was and if he knew me because he apparently thought that Derek was my boyfriend, and was making sure because he liked me. But I don't think this is the same case, since he didn't specifically mention /why/ he was asking my brother if he was related to me, and my crush isn't shy at all. I'm just confused.
Crush became friends with my brother? What does this mean?
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