This is correct. For an arbitrary and hypothetical example, imagine that Linus woke up yesterday and decided to convert the Linux kernel to an Apache licensed project. The long and almost impossible task would be to contact each and every contributor to the Linux kernel and ask for the permission to change the license of their contribution. The "short" and "easy" task would be to write a new kernel and replace all of Linux with it, applying the new license. The old Linux kernel would still be a GPL project, but moving forward any contributions would need to be Apache licensed.
It appears that the latter example is somewhat like what happened here. The old Oh-My-Fish project was some licensed project. It could have even been a WTF Public License[0] that _did_ allow contributors to fork and remove attribution. At some point, all the code in the repo was replaced with new code under the MIT license that served the same purpose, and the repo's name was changed. Moving forward, someone continued to merge in the new code to the old repo and tried to remove attribution to the new code, breaking the new code's license.
The Oh-My-Fish project could have done a classical fork, severing ties with the Wahoo project just before the merge of the re-written code happened and continue to work in isolation, but it seems that they did not.
[0] http://www.wtfpl.net