It just happens and I wouldn’t try to figure it out. Maybe the other student struck a chord with their particular admissions counselor. Maybe they had a voice that was unusual in their stack of people. A class full of identical students is really not all that interesting and the notion that a “regular” great student can’t keep up has just got to go away.
Example, my kids both went/go to schools in Virginia despite us being from California. My middle was just telling me about a class discussion on border security and how surprising he found it until he realized that none of his fellow students had ever actually known a dreamer or a family who was here illegally. His classmates weren’t being ugly or awful… they just had this picture of an immigrant in their mind that didn’t line up with our son’s practical experiences from attending a HS with many. Now, this isn’t to start a debate on immigration only to point out that they were able to have a diverse conversation because my son had something different to say based on where he came from. Kid B may have had something similar to offer.