It's still one iOS SDK. As a developer and power user audience, we remember when iPhone OS was first renamed to iOS on iPad's release because they were the same. It hasn't been renamed back. Regarding usage, the term iOS development within Apple dev shops still refers to both iPhone and iPad code and App Store distribution. We generally use iOS as an umbrella term, and reach for the new term iPadOS in reference to the iPad-exclusive parts of the user experience like its multitasking capabilities and Universal Control.