The chart specifically lists “proficient” and “advanced” at 12th grade. What do those words mean?
For “proficient”, the “inferences” and “interpretative statements” components will rule out most readers.
For reference, these are some of the skills that higher level SAT and GRE reading questions attempt to evaluate.
The way one could (somewhat crudely) relabel that data is “what percentage of 12 graders could plausibly read college-level texts”. Interestingly, the college attendance numbers match these percentages fairly closely.