Non-technical people don't always think of an OS as the computer OS. To them, sometimes it means more like standard operating procedure or process - a standard way of doing things.
Secondly, for tech products, calling yourself an OS, you are associating yourself with things like Windows, Mac or Linux. You are indirectly trying to grandstand and position yourself as meaningful enough to be an "OS" when clearly, that is far from what an app layer + AI/LLM on top of a real OS is.
The biggest giveaway is this, and I'm exposing it right here -from a technical perspective, what operating system computer technology was built from scratch from first principles around AI/LLM?
Someone wants to be the first company to get huge sums of money/funding to be that startup/project, so that is also a positioning tactic.
The issue is of course, most people are standing on the shoulders of giants at this point... and OS has this conflicted meaning with nontechnical users also about work process vs the software that runs my computer.