Eric on the BU board is the expert on this sort of stuff. Below is his explanation. Sounds like the NCAA may have cut him a break:
Generally (there are exceptions for military service, missions, et cetera), an international student-athlete only gets one year from the time he graduates high school until his college eligibility clock starts ticking. And as far as the NCAA is concerned Chuku graduated from high school three years ago. Hence the problem.
This is a fairly common problem with British athletes as they technically graduate from high school following 11th grade. So anyone staying in Britain until the completion of 12th grade (which is basically required if you want to attend college there) and then attending a US prep school for a year after that has exceeded his one year window. In Chuku’s case, he also sat out a year due to illness, so getting three years from the NCAA was good news. Technically, he should have only two.