This is pre release test software for internal purposes at Samsung. This is not the final version but more like work in progress.
Most likely a Samsung employee has "leaked" this. Leaks happen a lot. Take for example, Snowden and his NSA leaks, leaks happen all the time.
It's experimental software and does not reflect the final official version which Samsung will initially release via OTA updates. One Samsung employee took a risk in leaking this to the masses. In my time owning various Samsung phones it's common. It's a fully functional TouchWiz rom but like I said it does not represent the final version. Samsung like any other manufacturer work on updating their software and at times "employees" will leak the current software that is being worked upon.
It's no different to say a Chinese factory worker leaking information about the next iPhone by showing the cases prior to any official Apple announcement, or EV Leaks who are very good at obtaining information on upcoming devices, we live in a world were someone will take a risk to leak confidential information on software intended for internal purposes only or leak information in regards to whatever.
Phone: OnePlus One 64GB
Rom: SlimSaber | Der Kernel: AK
Tablet: Nexus 7 2013 32GB
Rom: SkimKat | Der Kernel: Stock SlimKat
Previous: HTC DesireHD | Samsung Galaxy SII | T-Mobile Rapport | Samsung Galaxy S (Backup) | Samsung Galaxy SIII | Samsung Galaxy Note II | HTC One X | Nexus 4 | Samsung Galaxy S4