Given Knuth's background, it may well be that he was looking for the (computationally) optimal solution, wherein the bash script was more about writing it quickly using existing tools.
1. Note that these were not quite "two solutions" as one might think from the phrase, but rather a commissioned program, and a review of it (which also happened to contain an alternative approach).
2. I did actually end up comparing them on a test corpus just last month -- kind of linked to it twice in the comment but here it is again: https://codegolf.stackexchange.com/questions/188133/bentleys... -- a C++ translation of Knuth's program runs about 140 times faster on the largest case than the shell solution.
3. About "writing it quickly using existing tools": note that while the Unix commands -- tr, sort, uniq, sed -- are widely available today (even on Windows!), they were not so in 1986, unless you were in certain special circumstances such as having paid a lot of money for a Unix system. So McIlroy was pointing out that in their (Unix) world, this problem would be easier than it was outside, so his proposed solution was also sort of an advertisement for Unix, not just the Unix philosophy.