That's the updated build of 9.2.1 to fix the Touch ID "Error 53" issue. There's no point updating (unless you have that particular issue with 3rd party home button replacements).Software update on iPhone says I'm up to date at 9.2.1 but iTunes says update available - 9.2.1
Odd.
View attachment 622227
https://www.macrumors.com/2016/02/18/apple-ios-9-2-1-error-53-fix/