Mistaken attribution, or taking something that doesn't belong to you and saying it belongs to someone else is a core function of copyright law and should not be confusing to anyone who has dealt with it before.

What is your understanding of what license and rights the author was providing them - understanding this I can figure out where you are confused.

He even asked them to force-push a new history because they got the name wrong!

Mistakes happen, I guess this hurts his 'commits in a public repo' cv score.

I didn't see any threat to sue. What's your source?