Their definition of "the platform" in the TOS is verbose and has weird grammar. I can see how people came away with a different understanding.

> User shall not translate, decompile or reverse-engineer the Platform, or engage in any other activity designed to identify the algorithms and logic of the Platform’s operation, unless expressly allowed by Arduino or by applicable license agreements;

> The Site is part of the platform developed and managed by Arduino, which allows users to take part in the discussions on the Arduino forum, the Arduino blog, the Arduino User Group, the Arduino Discord channel, and the Arduino Project Hub, and to access the Arduino main website, subsites, Arduino Cloud, Arduino Courses, Arduino Certifications, Arduino Docs, the Arduino EDU kit sites to release works within the Contributor License Agreement program, and to further develop the Arduino open source ecosystem (collectively, the “Platform”).

I can only read this as the entirety of "Arduino open source ecosystem" being part of "the Platform".