Gordy first catches Junior's attention in the classroom, after he corrects the teacher about misguided information concerning petrified wood. The teacher is relieved when Gordy, the class genius, raises his hand, because he assumes this student will put Junior in his place. Instead, Gordy agrees with Junior.
If you only read the scene from Junior's perspective, you might assume that Gordy becomes his friend because he is also strange and lonely. This is what Junior believes brings these two together. He approaches Gordy and describes with bluntness just how strange and different Gordy is from the rest of the kids at the school. Gordy uses phrases like "singular wit" and "Anglophile." Junior points out to Gordy that the two of them are both "weird" (93).
I mean, you and I, we have a lot in common.
Gordy studied me now.
I was an Indian kid from the reservation. I was lonely and sad and isolated and terrified.
Just like Gordy.
And so we did become friends. (94)
In this conversation, however, if you examine Gordy's responses to Junior, it is clear that Gordy does not care that he is different from others, nor does he feel ostracized nor lonely by this fact. Therefore, it could be argued that Gordy is merely intrigued by Junior, and finds him both intelligent and interesting. He might also enjoy the position of being able to teach someone who is willing to learn. Look at the progression of Junior's description of the friendship:
We didn't share secrets. Or dreams...No, we studied together.
Gordy taught me how to study.
Best of all, he taught me how to read...
...Gordy believed in me...
...he was the smartest person I'd ever known...
And he certainly helped me through high school. (94-98)
Gordy might not care at all that he is different from other kids. He seems to celebrate his own weirdness, or not really even notice it. But it is also clear that Junior is the first person to be interested in Gordy, therefore he is a live and listening outlet for Gordy to share his intellect with. Gordy very likely agrees to be Junior's friend because he enjoys the intellectual stimulation.