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.
Re:DMCA notice against oh-my-fish
by johnmaguire2013 on Friday September 25, 2015 @10:46AM
(#10278458)
Yes, I was the one who initially noted that he didn't comply with that clause. I was wondering whether the original creator could retroactively revoke the MIT license permanently from the guy who abused the license.
Or in fact, does the creator of the original project have the ability to say "I no longer offer this license to you"?