It's important to have clear terms for important concepts. If you mean source-available (aka "open box"), use that phrase instead. If you mean open source software, call it open source software. Although I don't think it applies in your case, in my experience many of the people who misuse the term "open source software" (OSS) to identify something that is NOT OSS are expressly trying to deceive. Hopefully we can agree that fraud is not acceptable, and then move on to discuss whether or not this is (intentional) fraud.
The term "open system" was not well-defended years ago. It has a definition, but vendors wanted to redefine it into its opposite. Eventually "every vendor with an open mouth had an open system", making the term "open system" mostly useless. It is reasonable to defend clear definitions of important terms, because otherwise communication breaks down.