It sounds as if there are a number of takes on what is referred to as a bilingual IB program. It's interesting to hear the specifics of how it is done at your child's school. Anyone else want to chime in?
In our case, our child is enrolled at a bilingual K-12 school, so everybody is completely fluent in at least two languages. No child can enroll after kindergarten at the school unless they are already fluent, since 50-80% of their classes are taught in another language (such as math, science, history, etc). Once they reach high school age, only those completely fluent in both languages can go on to get a bilingual IB.
Kids who enroll in the high school and are not completely fluent in the second language can only opt for the English-only IB. Of course, even the English-only IB kids must take a foreign language class for at least a couple of years, just like any other high schooler. But all the classes they take for the IB, except for that one foreign language class, are taught in English...a completely different experience than for those who get the bilingual IB.