This is an interesting take. I think if they continued to any new wahoo code after the disagreement and breaking up, then that new code is infringing. However, the agreed upon merge code might not be subject to the DMCA.
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.My point is that if they agreed to merge projects and wahoo didn't keep their license on it, then that code at the time of agreement is no longer under the exclusive copyright of the wahoo author.