I don't think "blameless" means nobody can ever be held responsible if they actually did something truly malicious, negligent, etc. It's that the point of the investigation is to improve the system rather than assign blame. This is in stark contrast to the post by 'colechristensen assuming that someone must be responsible and that they should be "stomped for negligence".

I do think the person you're responding to phrased it poorly though. While a blameless investigation can result in someone being held liable (i.e. "blamed"), an equally valid result could be that nobody is blamed when no individual liability is warranted by the facts.