CE based races pre-qualify riders based on previous performances (any rides) - in this case, his previous rides/workouts and race would have been lower enough to be a legit Cat C racer (in CE events). Note that the avg of ZP top 3 95% results over 90 is ZP Cat method, not CE (read the first post in this thread if you want to know more about CE)
New riders that haven’t pushed themselves, or riders that haven’t pushed themselves for 60 days at least, are always going to be capable of sandbagging. In this case, he is new. He is also now a ZP Cat B and I would be stunned if is not also now a CE Cat B (as a few others in that race should be).