Sorry it's about 34 minutes in, when I started to head towards the burnt Forest and arrived at basecamp. All hell broke loose.
Yeh, I agree with Arez there, can't say much from that clip other than "you got a screamer and you let her scream".
Before the screamer, the situation looked rather normal, couple zeds, couple dire wolves.
After the screamer, well, it looked normal as well. If you don't kill it, you'll have a party on your hands. Screamers beget screamers and you'll have an infinite horde.
I can't remember how heat works in unloaded chunks; your stations will work on, but will they just gather heat, or will it also cool down?
Anyhoo. You need 20 heat for a chance at a screamer, just turning on a campfire generates 5. 15 more from gunfire, I wouldn't have though you shot enough for 15, but it isn't far off.
But, you went past the threshold, got a screamer, and didn't deal with her fast. Can't say anything about the area spawns from that.
To protect yourself from screamer hordes, you'll either need real fast killing (dead within a couple seconds from when she sees you), or you want to hide behind full blocks and let any form of trap take care of her. Full blocks, since partial blocks don't work properly with line-of-sight, zeds can see through even those half blocks you're standing on.