Nope, I made a mistake there. It's good practice, when copying code from software with a different license, to call out what code is copied from where, but such a thing is not mandatory.

So... what would be the minimal, right thing to do here?

I'd say one of the things you have suggested. Copying the license file from spegel into a SPEGEL_LICENSE file in the repository would be sufficient. So would be actually crediting the project properly in the README with something like "portions of this code were taken from the Spegel project, under the MIT license" with a following copy of the MIT license.

Feels like opening a PR doing that would be faster than writing a blog post to complain.

You could open the PR and it would also be faster than writing all these comments here about opening a PR.

That's not the point, it is not the author's duty to do that and him pointing out Microsoft's wrongdoing is meaningful at least to me because I will be more cautious if I'm ever being approached in a similar way.

> Microsoft's wrongdoing is meaningful at least to me because I will be more cautious if I'm ever being approached in a similar way.

That's the thing: Microsoft approaching the author has nothing to do with the wrong attribution. And I am not sure if the original author here is frustrated because of the wrong attribution or just because they would have hope money and fame from the fact that Microsoft reused their code.

Because it's not like Spegel lacks visibility (given the numbers they shared in the article), the link on Peerd's README is probably not bad for Spegel, and the attention here is publicity again. Probably infinitely more than if Microsoft had done the attribution correctly.

Only the author knows about his motives.

Your point seems to be that the author should not have written the blog post and done a PR instead.

My point is that whatever the authors motives are and whether he did a PR or not, his blogpost was informative to me and has value on its own.