Peekay4 :
I'm speculating that -- at the time -- neither the pilots, Air Canada, nor the controller had an appreciation of just how close they were to disaster, until the tapes were reviewed.
The pilots probably thought they'd just need to file a safety report in the morning and that would be the end of it.
And I think you are probably right. Lining up with taxi way or wrong runway is not that unusual. It is the media coverage of one case that makes it sensational.
In Frankfurt ( Germany) for instance such incidents are a few per year, we even had an actual landing in the centre taxiway ( an Antonov 124 !) some 20 years ago, and a take off from the same centre one , a couple of years ago. In both cases as no-other aircraft was taxing at the time on it, no news coverage .