O_o this happened to me today.
Except it was some girl who sat next to me at lunch. And she wasnt wearing a Homestuck shirt. But she was wearing a shirt, just not a homestuck shirt. Its one of those do-gooders who see me sitting alone and decide to invite me to sit with them.
I usually decline because when I accept its just super akward. Like the girl that the only thing she knew about me was that I was in pre ap english. And she said "We can Talk about english" I actually can talk about english for a bit. But it made me laugh that was her entire perception of me.
Or maybe she just likes you and is trying to show you have something in common. It's just an excuse to talk to you, not necessarily that she sees you only as "that guy from english". Of course it's also possible she just needs help in that regard and knows you're good at it too. Guess you won't know until you go talk to her, huh?
Also found the "but she was wearing a shirt" pretty funny.