Not foolhardy at all.
Claiming IU would have made the field is based on the data available at the time. It isn't like the season was cancelled in December. The regular season was over, only the conference tournaments were left.
Since IU was in 89 of the 90 predicted brackets, that would indicate that the chances of IU being in the big dance are very high. Also, the brackets I checked, IU was not among the final four in. That would indicate to me that IU was not "on the bubble".
Could a scenario be concocted where IU was out? Absolutely. I am sure that with certain teams getting upset conference tournament titles and IU getting blasted by Wisconsin, IU would have been out.
In other words, IU was not a "lock" for the tournament but since they were not in the last four in, the number of things that would had to go wrong for them to be out leads one to conclude that they were in.