Correct. However, a given instruction set, protocols for interconnected hardware, and APIs to support development do together constitute a platform.
Any OS running on any circuit board is not a platform.
Then you might as well call your platform "technology" because every circuit board and every device in the world is using the same loose confederation of standards.No. For instance, despite sharing a common architecture, it's very easy to yell the difference between iOS and Android as platforms. They have very different APIs and networked services, such that code written for one won't work without some sort of intermediary.