Because he's Indian, Raj stands out from all of the white people in his tennis club. And he's desperate to not be the only one that looks different. When an African-American couple interview to join the TC, he's already envisioning their friendship, their children being friends and so he says something he really shouldn't. In many regards Raj comes off as too desperate, but is certainly a reflection of a society that many of us find ourselves navigating right now - the motivations for personal connections and the difficulty in finding the right thing to say to connect and not offend.