The only text on that page that states the origin of the dev's code is Mazda's claim that the relevant code is Mazda's. If their claim is true, then it would seem to me the DMCA takedown is valid.

The reason the DMCA takedown notice is malicious is that code from Mazda's official app is not required to develop a tool that works in a similar way. The API of the server is freely accessible and figuring out how to interact with it can be done completely without infringing on anyone's copyright.

Okay, it doesn't matter how it could have been done, it matters how it was done, and again, the only claim made on the page is that it was stolen code.

I'm all for actually owning what you buy and being able to integrate it with your other stuff however you please, but distributing someone else's work is a valid claim for infringement. And as with any other cloud-based stuff, don't expect it to work forever. Support and push for local device access without the need for cloud services.