My guess is that AIR was installed by another application at some point (possibly Acrobat.) If you uninstall it, you should get a dialog with a complete list of apps that rely on AIR. It warns you that if you continue the uninstall, those apps will no longer function.
However, since you've recieved the AIR update dialog you are actually "using" an AIR based application. If you're willing to keep AIR installed, you should be able to update safely by following the dialog instructions.