Aurora as a Sailfish OS fork has been developed by Jolla, a Finnish company. Aurora a "fork" of Sailfish OS because it isn't the entire Sailfish OS, but rather, a portion of Sailfish combined with other features. Think of a "Sailfish fork" as you would an "Android fork."
In Android, AOSP (Android Open Source Project) allows anyone to develop their own take on Android. Google has done this, as its app suite includes Gmail, Google Docs, Google Maps, Google Drive, Google Calendar, Google Play, Google Play Music, Google Play Movies, and so on.
None of these Google apps are part of AOSP but are Google's own take on Android. Someone else, Huawei, for example, could use AOSP and produce an entirely different suite of apps. In fact, Huawei uses a forked version of Android in China that does not contain Google apps.
Aurora, in this vein then, is a Russian take on a Finnish mobile operating system. Since Finland and Russia are two different countries with two different sets of needs in a mobile OS, some things remain the same between the original Sailfish OS and the forked Aurora version, while some things change.
Russia can choose to add its own suite of apps to Aurora, whereas, if Russia used the original Sailfish OS, it would be forced to respect Finland's own app suite and leave it intact. Forked versions of operating systems allow those who use them to "carve" them up as they please.
Sailfish is an independent OS developed by Finnish company Jolla that is Linux-based. Jolla has a heritage in MeeGo OS and Finnish OEM Nokia (the brand name now owned by HMD Global). MeeGo OS was an earlier OS crafted by Intel and Nokia.
It has now matured in its third generation (Sailfish 3), bringing privacy features such as enterprise Wi-Fi, data encryption, Mobile Device Management (MDM), fully integrated VPN solutions, USB On-The-Go storage, and is a secure OS that is compatible with Android applications though it remains fully independent from Android. Sony Xperia users can download Sailfish 3 at sailfishos.org.
Aurora's Android compatibility would meet the technical hurdle of Huawei's own ARK OS at the moment. ARK OS isn't yet fully compatible with Android apps, meaning that Huawei customers would be forced to adjust to a new OS without Android should Huawei sell ARK OS on its mobile devices.
Aurora (Sailfish) would ensure Android compatibility. Additionally, it would put the Google argument to rest that a forked version of Android, sans Google apps, would be "less secure" than Google's Android. Since Aurora (Sailfish) is designed for governments and corporations, it would possibly have more enterprise encryption than Google's Android.
Aurora is a Sailfish OS fork. And yet, "Aurora" as the Russian name for it is fairly new. Jolla's own website (that is, Jolla, the Sailfish OS creator) says that Russian national operator Rostelecom re-branded Sailfish OS as "Aurora" since February of this year. Russia intends to switch all its government officials over to Aurora by 2021, the post says. Originally, Sailfish OS is "Finnish," and is still called "Sailfish" in Finland; and Aurora is the Russian forked version that now has an official Russian name.
Huawei finds itself in a desperate situation to continue making and shipping mobile devices. Since its Android license was revoked by Google last month, just days after President Donald Trump handed down his ban on Huawei and added its name to the Entity List (thereby forbidding American companies from doing business with the corporation), the Chinese OEM finds itself without an OS for its upcoming devices. Since its Android license is revoked, there will be no Android Q (Google's upcoming system update) for Huawei phones, tablets, and smartwatches.
Huawei has considered its own ARK OS, but for the reason above, finds it to be insufficient. The company could provide its own forked version of Android for non-Chinese customers, as it does in China (sans Google apps, of course). Sailfish would be another route to Android compatibility and security, both of which matter to consumers in this privacy-driven age.
Huawei is also considering using its own app store, AppGallery, for its own forked Android experience, or going with a Play Store alternative such as Aptoide (which has been used as an app store on some Android smart projectors).
All these options at the moment indicate that Huawei is searching for the ideal solution to keep growing its financial fortune. Which one will win out is a matter of wait-and-see.