While there is no way to know for sure if this is true, there are several reasons why it might not be too ludicrous. This is because over the past few years, we’ve seen Apple take steps to rebrand its operating systems. macOS used to be known as OS X, and Apple had also later introduced iPadOS, tvOS, and also watchOS, so for the company to rebrand iOS to call it iPhone OS doesn’t seem too much of a stretch.
We should also point out that platforms like tvOS, watchOS, and iPadOS are essentially forks of iOS. This can create some confusion as technically, devices like the iPad still fall under iOS, so sometimes referring to iOS for the iPhone might be a tad confusing. By calling it iPhone OS, it would make it much more obvious as to which OS Apple is referring to.
iPhone OS.
— jon prosser (@jon_prosser) June 18, 2020
It is unclear if iOS will still stick around and be the general term for Apple’s platform, or if it will go away completely and we’ll be getting separate names for separate products. Either way, this should be revealed at Apple’s upcoming WWDC 2020 event which will take place next week, so until then, take it with a grain of salt.