Tzadeck

He can't. Even if he authored all of the code in OhMyFish/Wahoo, which maybe be the case, the OhMyFish folk can rightly use the entire source of Wahoo granted they comply to the MIT license, which they didn't hence the DMCA takedown:

    The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

Or just use https://github.com/wa/wahoo

Actually, the author of Wahoo was also from both, an ethical point of view, author of OMF having contributed more than half of the code and from a legal point of view as an administrator in the GitHub repository. He himself merged his own PR. The problem is he and the other collaborators had "disagreements" and decided to split. He would return to Wahoo and the OMF folks would return to pre-Wahoo OMF. What actually happened is that a new project was created with the same name "oh-my-fish" and the old git history was simply pushed to the new repo. The LICENSE was also changed attributing the copyright to Bruno, the other OMF admin folk.

If oh-my-fish properly included the copyright and permission notice of the MIT license, then they are within the bounds of the license. It doesn't matter what the author's requests are, they can use it if they attribute properly. But they failed to do so and the creator's copyright was not credited, so they are in violation of MIT, which is pretty lame considering how easy it is to use MIT code in a compliant way. I am afraid this DMCA is legit.

Yes, but you missed the nuts and bolts of MIT subject to the following conditions:

    The above copyright notice and this permission notice shall be included in all
    copies or substantial portions of the Software.

In the DMCA it's stated that his copyright is not credited, so they are in violation of MIT. Which is what is happening here.

Before Wahoo, the DMCA filer worked as an OMF core member, and months later created Wahoo, which is a totally different project. Eventually all collaborators decided to reunite, and the code base was completely replaced with wahoo, sans the name, but due to "disagreements" they split. The project actually has a long history.