Directly below that table, the documentation explain how those values were developed:
"Technical Notes: We simulated 1000 respondents answering randomly to each questionnaire, then estimated the scores using HB: prior variance=2, d.f.=5. Both "best" and "worst" answers were simulated for each respondent (with the exception of the 2 items case). For each simulated data set, we sorted the respondents' fit statistics from highest to lowest and recorded the 95% percentile fit. If asking only "bests," because the amount of information for each respondent is reduced, the Suggested Minimum Fit would be higher."