https://www.eurogamer.net/articles/2017-01-18-did-nintendo-d...
The company is extremely micromanaged and pedantic, and this is not the kind of thing that could possibly be overlooked at Nintendo.
Specifically, the "iNES header", originally created by Marat Fayzullin for use with his NES emulator, iNES[1].
If you look at the iNES manual[2], way down at the bottom in the changelog for version 0.7, you can see "Sound support completely rewritten, thanks to Kawase Tomohiro".
If you search the Internet for Kawase Tomohiro, you'll find[3] somebody by that name seems to work for Nintendo as a programmer, and in particular worked on the NES emulator used in 2001's Animal Crossing.
Of course, that's not conclusive evidence, but given the competing claims "Nintendo, a notoriously uptight company, has been downloading pirate ROMs to sell" versus "Nintendo hired a pioneer of NES emulation to work on their emulators, who kept using the tools and formats he was used to", I feel like one is more likely to be true and the other is more likely to get ad impressions.
[1]: https://fms.komkon.org/iNES/
