Apple only allows reverting to a previous software version, if it's still signed by them. At this moment, the ones available are 9.2 (the most recent) and 9.1 (the one before 9.2). Both can't be jailbroken at the moment.
If you try to install a different iOS, not signed by Apple, you'll get an error, and it will be impossible to proceed. The reason why it's working that way, is because iTunes/your iPhone is connecting to Apple's servers while installing the software, to make sure the right one will be installed.