New region suddenly received during Lougiones campaign

[azayrahmad]

I'm playing Lougiones campaign and a couple years in after I conquer Scurgum and Waldawa I suddenly got a new region, Gallwagardas (west of Waldawa). No notification as far as I remember, it's just suddenly belong to me. There is no governor in place, only six units of soldiers. My family members are already stretched thin so I haven't been able to send one to govern.
Also at the same time Kimmerios Bosporos became my enemy, even though we have no neighboring region and nobody ever attack anybody. A couple years after that Bosporos asked for ceasefire and asked for the region back. I counteroffered with only ceasefire and Bosporos happily accepted. Gallwagardas is still mine and I just left it alone to generate revenue.
So what happened there? Is it a scripted event or a bug?

[QuintusSertorius]

Not scripted, not a bug. That was a revolt, which happened to be in your favour, from the Bosporans.

[azayrahmad]

Oh wow, lucky me. Never knew that revolt could result in anything but Eleutheroi, let alone in my favor. So is this completely random or is there any contributing factor to them joining me? Like the fact that the region is neighboring mine or perhaps because I happened to place an agent there?

[Lusitanio]

I'm not sure but I think it has to do with the fact that your culture is predominant in that region.