Pretty sure the right move as soon as he said "I didn't write that" was to just say. "It isn't important who wrote it, we all make mistakes, let's see together how we could have done better."

Today, I would maybe agree and have grown wiser. But software engineering is 50% failure management. And admitting failure should be normal for every level, I am very open and outspoken that I (just as every other guy) makes errors all day. We literally have error management system in place because of that - Bugtrackers, Test pyramid, QA departments etc. It is simple not helpful if people not take accountability and grow on their mistakes.

Pretty sure that can be the wrong move in an instance where it does matter who wrote that. Freely allowing derogation of authorship soon fosters derogation of responsibility.

Mistakes are allowed is a good lesson. Lying is allowed is a bad lesson.