@FarmerJayhawk
You are correct that basketball, football and volleyball are headcount sports. That means that they have a certain number of scholarships and cannot split those scholarships up between players. This means that whoever the people are on scholarship, they are on full scholarship. You can’t give one guy a half a scholarship, and another guy a half a scholarship like you can in baseball or track or other sports.
However, an athlete can play more than one sport while in college. Because you cannot double dip, you have to take a scholarship in your “primary” sport. Bo Jackson, for instance, played football, baseball and ran track at Auburn. However, he was on a football scholarship, which allowed the baseball and track programs to have an elite level player as a walk on for their programs since he could not also be on scholarship for those programs.
Perhaps a better example is Santana Moss at the University of Miami. When Miami was on probation in the late 1990’s they had scholarship limits as a penalty in football. Moss was also an elite level HS track star (state titles in long jump and triple jump, ran a 10.7 100 in college), so Miami gave him a track scholarship initially. There was some controversy because people argued that Moss wasn’t really a track athlete, but he participated in track all four years at Miami and even won the conference title in the triple jump as a senior. He didn’t initially count against the football scholarship limits because he accepted the track scholarship.
McKinstry would be in the same type of situation. He is an elite football player, and a good basketball player. He would be on football scholarship, but, as @Texas-Hawk-10 mentioned, part of the recruiting pitch could be to come and be a part of an elite level basketball program as a preferred walk on. Yes, KU offered a hoops scholarship, but that is part of the pitch to let him know he would be able to play both at KU. I doubt Alabama or Auburn makes the same offer, so if the young man wants to play both, KU is probably his choice. And he’s a legit D1 prospect in basketball, so he could play at KU.