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.
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.