The demo shows a very clearly written bug report about a matrix operation that’s producing an unexpected output. Umm… no. Most bug reports you get in the wild are more along the lines of “I clicked on on X and Y happened” then if you’re lucky they’ll say “and I expected Z”. Usually the Z expectation is left for the reader to fill in because as human users we understand the expectations. The difficulty in fixing a bug…
Since this fixes 12% of the bugs, the authors of the paper probably agree with you that 100-12= 88%, and hence "most bugs" don't have nicely written bug reports.