I expect more from Caltech that having such an obvious typo in their graphic. Note that an ACT score of 33 is both bucket B and bucket C.
I’m not sure what Caltech is trying to accomplish with the system. The linked page makes it sound the system is intended to show students that they do not need perfect scores. If so, it only suggests to kids that they need a 780+ SAT or 35+ ACT and can stop re-testing once they cross that almost, but not quite perfect threshold. It may give the impression that a 770 SAT / 34 ACT on EBRW/English/Reading won’t cut it. I’m skeptical that this system will have any notable benefit over a traditional non-bucket implementation.