This is a very minor, nigh silly, project but this sort of wanton bifurcation hurts open source's reputation and is already a huge problem in the Node community.
Then, your choice of words is not ideal:
>NOTE: I no longer actively maintain this package. I'd love to get PRs to keep it going though!
If it's not maintained anymore then I as a developer don't really gain anything (bugfixes, features) by submitting a PR vs. just forking myself. So the choice to fork is understandable, even if it's not what you intended to happen.
[1] https://arstechnica.com/information-technology/2014/10/how-d...
I think the issue is less about license and more about what is good form and helps to keep the ecosystem a bit less cluttered.
Forking is fine, merging two packages is fine, removing the authors name from the license (while leaving his name all over the rest of the package, which shows that there is no malicious intent, merely some confusion) is not.